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was very noticeable in the later life of Princess Alice. After the marriage of the Princess Royal in 1858, the new responsibilities devolving upon Princess Alice, as the eldest daughter at home, called forth the higher traits of her character, and brought her into still closer relationship with her parents, and especially with her father. In the summer of 1860, at Windsor Castle, Princess Alice first met her future husband, Prince Louis of Hesse. An attachment quickly sprang up, and on the prince’s second visit in November they were formally engaged. In the following year, on the announcement of the contemplated marriage, the House of Commons unanimously voted a dowry of £30,000 and an annuity of £6000 to the princess. In December 1861, while preparations were being made for the marriage, the prince consort was struck down with typhoid fever, and died on the 14th. Princess Alice nursed her father during his short illness with the utmost care, and after his death devoted herself to comforting her mother under this terrible blow. Her marriage took place at Osborne, on the rst of July 1862. The princess unconsciously wrote her own biography from this period in her constant letters to Queen Victoria, a selection of which, edited by Dr. Carl Sell, were allowed to be printed in 1883. These letters give a complete picture of the daily life of the duke and duchess, and they also show the intense love of the latter for her husband, her mother and her native land. She managed to visit England every year, and it was at her special request that when she died her husband laid an English flag upon her coffin.
In the war between Austria and Prussia in 1866, HesseDarmstadt was upon the side of the Austrians; Prince Louis accompanied his troops to the front, and was duly appointed by the grand-duke to the command of the Hessian division. This was a time of intense trial to the princess, whose husband and brother-in-law, the crown prince of Prussia, were necessarily fighting upon opposite sides. The duke of Hesse also took part
,in the principal battles of the Franco-Prussian war, while the duchess was actively engaged in organizing hospitals for the relief of the sick and wounded. The death of the duke’s father, Prince Charles of Hesse, on the 20th of March 1877, was followed by that of the grand-duke on the 13th of June, and Prince Louis succeeded to the throne as Grand Duke Louis IV. In the summer of 1878 the grand-duke and duchess, with their family, came again to England, and went to Eastbourne, where the duchess remained for some time. She returned to Darmstadt in the autumn, and on the 8th of November 1878 her daughter, Princess Victoria, was attacked by diphtheria. Three more of her children, as well as her husband, quickly caught the disease, and the youngest, “ May,” succumbed on the 16th. On the 7th of December the princess was herself attacked, and, being weakened by nursing and anxiety, had not strength to resist the disease, which proved fatal on the 14th of December, the seventeenth anniversary of her father’s death. She left one son‘and four daughters.
See Carl Sell, Alice: Mitlheilun en aus ihrem Leben and Briefen, &c. (Darmstadt, 1883), with En lish translation by the Princess Christian, Alice: biographical sketc and letters (1884). (G. F. B.)
ALIDADE (from the Arab), the movable index of a graduated are, used in the measurement of angles. The word is used also to designate the supporting frame or arms carrying the microscopes or verniers of a graduated circle.
ALIEN (Lat. alicnus), the technical term applied by British constitutional law to anyone who does not enjoy the character of a British subject; in general, a foreigner who for the purposes of any state comes into certain domestic relations with it, other than those applying to native-born or naturalized citizens, but owns allegiance to a foreign sovereign.
English law, save with the special exceptions mentioned, admits to the character of subjects all who are born within the king’s allegiance, that is, speaking generally, within the British dominions. In the celebrated question of the past-nati in the reign of James I. of England, it was found, after solemn trial, that natives of Scotland born before the union of the crowns were aliens in England, but that, since allegiance is to the person of the king, those born subsequently were English subjects. A child
born abroad, whose father or whose grandfather on the father’s side was a British subject, may claim the same character unless at the time of his birth his father was an attainted traitor, or in the service of a state engaged in war against the British empire (4th Geo. II. c. 21). Owing to this exceptional provision some sons of Jacobite refugees born abroad, who joined in the rebellion of 1745, were admitted to the privilege of prisoners of war.
It has been enacted in the United Kingdom with regard to the national status of women and children that a married woman is to be deemed a subject of the state of which her husband is for the time being a subject; that a natural-born British woman, having become an alien by marriage, and thereafter being a widow, may be rehabilitated under conditions slightly more favourable than are required for naturalization; that where a father or a widow becomes an alien, the children in infancy becoming resident in the country where the parent is naturalized, and being naturalized by the local law, are held to be subjects of that country; that those of a father or of a widow readmitted to British nationality or who obtains a certificate of naturalization, becoming during infancy resident with such parent in the British dominions in the former case or in the United Kingdom in the latter, become readmitted or naturalized (Naturalization Act 187o,s. 10). The nationality of children not covered by these enactments is not aflected by the change of their parents’ nationality. The same statute provides that a declaration of alienage before a justice of peace or other competent judge, having the effect of divesting the declarant of the character of a British subject, may be made by a naturalized British subject desiring to resume the nationality of the country to which he originally belonged, if there be a convention to that effect with that country; by natural-born subjects who were also born subjects of another state according to its law; or by persons born abroad having British fathers.
Naturalization, which means conferring the character of a subject, may now, under the act of 1870, be obtained by applying to the home secretary and producing evidence of having resided for not less than five years in the United Kingdom, or of having been in the service of the crown for not less than five years, and of intention to reside in the United Kingdom or serve under the crown. Such a certificate may be granted by the secretary of state to one naturalized previously to the passing of the act, or to a British subject as to whose nationality a doubt exists, or to a statutory alien, Le. one who has become an alien by declaration in pursuance of the act of 1870.
In the United States the separate state laws largely determine the status of an alien, but subject to Federal treaties. (For further particulars see ALLEGIANCE and NATURALIZATION.)
Many of the disabilities to which aliens were subject in the United Kingdom, either by the common law or under various acts of parliament, have been repealed by the Naturalization Act 1870. It enables aliens to take, acquire, hold and dispose of real and personal property of every description, and to transmit a title to it, in all respects as natural-born British subjects. But the act expressly declares that this relaxation of the law does not qualify aliens for any office or any municipal, parliamentary or other franchise, or confer any right of a British su‘bject other than those above expressed in regard to property, nor does it affect interests vested in possession or expectancy under dispositions made before the act, or by devolution of law on the death of any one dying before the act. A ship, any share in which is owned by an alien, shall not be deemed a British ship (Merchant Shipping Act 1894, s. 1). By the Juries Act 1870, s. 8, aliens who have been domiciled for ten years in England or Wales, if in other respects duly qualified, are liable to serve on juries or inquests in England or Wales; and by the Naturalization Act 1870, s. 5, the aliens’ old privilege of being tried by a jury de medietale linguae (that is, of which half were foreigners), was abolished.
It seems to be a rule of general public law that an alien can be sent out of the realm by exercise of the crown’s prerogative; but in modern English practice, whenever it seems necessary to expel foreigners (see EXPULSION), a special act of parliament has to be obtained for the purpose, unless the case falls within the extradition acts or the Aliens Act 1905. The latter prohibits the landing in the United Kingdom of undesirable alien steerage passengers, called in the act “ immigrants,” from ships carrying more than twenty alien steerage passengers, called in the act “ immigrant ships ”; nor can alien immigrants be landed except at certain ports at which there is an “immigrant officer,” to whom power of prohibiting the landing is given, subject to a right of appeal to the immigration board of the port. The act contains a number of qualifications, and among these empowers the secretary of state to exempt any immigrant ship from its provisions if he is satisfied that a proper system is maintained to prevent the immigration of undesirable persons. The principal test of undesirableness is not having or being in a position to obtain the means of supporting one’s self and one’s dependents, or appearing likely from disease or infirmity to become a charge on the rates, provided that the immigrant is not seeking to avoid prosecution or punishment on religious or political grounds, or persecution, involving danger of imprisonment or danger to life or limb, on account of religious belief. Lunatics, idiots, persons who from disease or infirmity appear likely to become a detriment to the public otherwise than through the rates, and persons sentenced in a foreign country for crimes for which they could be surrendered to that country, are also enumerated as undesirable. Power is also given to the secretary of state to expel persons sentenced as just mentioned, or, if recommended by the court in which they have been convicted, persons convicted of felony or some ofience for which the court has power to impose imprisonment without the option of a fine, or of certain ofiences against the police laws; and persons in receipt of any such parochial relief as disqualifies for the parliamentary franchise, or wandering without ostensible means'of subsistence,orliving under insanitary conditions due to overcrowding. (1N0. W.)
ALIENATION (from Lat. alienus, belonging to another), the act or fact of being estranged, set apart or separated. In law the word is used for the act of transfer of property by voluntary deed and not by inheritance, In regard to church property the word has come to mean, since the Reformation, a transfer from religious to secular ownership. “ Alienation” is also used to denote a state of insanity (q.v.).
ALIEN-HOUSES, religious houses in England belonging to foreign ecclesiastics, or under their control. They generally were built where property had been left by the donors to foreign orders to pray for their souls. They were frequently regular “ priories,” but sometimes only “ cells,” and even “ granges,” with small chapels attached. Some, particularly in cities, seem to have been a sort of mission-houses. There were more than too in England. Many alien-houses were suppressed by Henry V. and the rest by Henry VIII.
ALIENIST (Lat. alienus, that which belongs to another, Le. is external to one’s self), one who specializes in the study of mental diseases, which are often included in the generic name “ Alienation.” (See Insanrrr.)
ALIGARH, a city and district of British India in the Mcerut division of the United Provinces. The city, also known as Koil, Was a station on the East Indian railway, 876 m. from Calcutta. Sir Sayad Ahmad Khan, K.C.S.I., who died in 1898, founded in 1864 the Aligarh Institute and Scientific Society for the translation into the vernacular of western literature; and afterwards the Mahommedan Anglo-Oriental college, under English professors, with an English school attached. The college meets with strong support from the enlightened portion of the Mussulman community, whose aim is to raise it to the status of a university, with the power of conferring degrees. The population (1901) 70,434, showed an increase of 14% in the decade. There are several flour-mills, cotton-presses and a dairy farm. Aligarh Fort, situated on the Grand Trunk road, consists of a TCSUlfi-r polygon, surrounded by a very broad and deep ditch. It became a. fortress of great importance under Sindhia in 1759, and was the depot where he drilled and organized his battalions in the European fashion with the aid of De Boigne. It was mptured from the Mahrattas under the leadership of Perron, another French officer, by Lord Lake’s army, in September 1303, since which time it has been much strengthened and
improved. In the rebellion of 1857 the troops stationed at Aligarh mutinied, but abstained from murdering their officers, who, with the other residents and ladies and children, succeeded in reaching Hathras.
4 The district of Aligarh has an area of 1057 sq. m. It is nearly a level plain, but with a slight elevation in the centre, between the two great rivers the Ganges and Jumna. The only other important river is the Kali Nadi, which traverses the entire length of the district from north-east to south-west. The district is traversed by several railways and also by the Ganges canal, which is navigable. The chief trading centre is Hathras. In 1901 the population was 1,200,822, showing an-increase of 15% in the decade, due to the extension of irrigation. There are several factories for ginning and pressing cotton.
ALIGNMENT (from Fr. 0 and ligne, the Lat. linen, a line), a setting in line, generally straight, or the way in which the line runs; an expression used in surveying, drawing, and in military arrangements, the alignment of a regiment or a camp meaning the situation when drawn up in line or the relative position of the tents. The alignment of a rifle has reference to the way of getting the sights into line with the object, so as to aim correctly. ‘
ALIMENT (from Lat. alimenl-um, from alerc to nourish), a synonym for “food,” literally or metaphorically. The word has also been used in the same legal sense as ALIMONY (q.v.). Aliment, in Scots law, is the sum paid or allowance given in respect of the reciprocal obligation of parents and children, husband and wife, grandparents and grandchildren, to contribute to each other’s maintenance. The term is also used in regard to a similar obligation of other parties, as of creditors to imprisoned debtors, the payments by parishes to paupers, &c. Alimentary funds, whether of the kind above mentioned, or set apart as such by the deed of a testator, are intended for the mere support of the recipient, and are not attachable by creditors. .
ALIMENTARY CANAL, in anatomy. The alimentary canal, strictly speaking, is the whole digestive tract from the mouth to the anus. From the one orifice to the other the tube is some 25 to 30 ft. long, and the food, in its passage, passes through the following parts one after the otherz—mouth, pharynx, oesophagus, stomach, small intestines, caecum, large intestines, rectum and anus. Into this tube at various points the salivary glands, liver and pancreas pour their secretions by special ducts. As the mouth ((1.11.) and pharynx (q.v.) are separately described, the detailed description will here begin with the oesophagus or gullet. ,
The oesophagus (Gr. o't'am, I will carry, and ¢wyetv, to eat), a muscular tube lined with mucous membrane, stretches from the lower limit of the pharynx, at the level of the cricoid cartilage, to the cardiac orifice of the stomach. It is about IO in. long (25 cm.) and half to one inch in diameter. At first it lies in the lower part of the neck, then in the thorax, and lastly, for about an inch, in the abdomen. As far as the level of the fourth or fifth thoracic vertebra it lies behind the trachea, but when that tube ends, it is in close contact with the pericardium, and, at the level of the tenth thoracic vertebra, passes through the oesophageal opening of the diaphragm (q.v.), accompanied by the two vagi nerves, the left being in front of it and the right behind. In the abdomen it lies just behind the left lobe of the liver. Both in the upper and lower parts of its course it lies a little to the left of the mid line. Its mucous membrane is thrown into a number of longitudinal pleats to allow stretching.
The stomach (Gr. arbpaxos) is an irregularly pear-shaped bag, situated in the upper and left part of the abdomen. It is somewhat flattened from before backward and so has an anterior and posterior surface and an upper and lower border. When moderately distended the thick end of the pear or fundus bulges upward and to the left, while the narrow end is constricted to form the pylorus, by means of which the stomach communicates with the small intestine. The cardiac orifice, where the oesophagus enters, is placed about a third of the way along the upper border from the left end of the fundus, and, between it and the pylorus, the upper border is concave and is known as the lesser curvature. From the cardiac to the pyloric orifice, round the lower border, is the greater curvature. The stomach has in front of it the liver (see fig. 1), the diaphragm and the anterior abdominal wall, while behind it are the pancreas, left kidney, left adrenal, spleen, colon and mesocolon. These structures form what is known as the stomach chamber. When the stomach is empty it contracts into a tubular or'gan _which is frequently sharply bent, and the transverse colon ascends to occupy the vacant part of the stomach chamber.
The last inch of the stomach before reaching the pylorus is
outer longitudinal. The peritoneal coatis described in the article on the coelom and serous membranes.
The small intestine is a tube, from 22 to 25 ft. long, beginning at the pylorus and ending at the ileo-caecal valve; it is divided into duodenum, jejunum and ileum.
The duodenum is from 9 to 11 in. long and forms a horseshoe or C-shaped curve, encircling the head of the pancreas. It diflers from the rest of the gut in being retroperitoneal. Its first part is horizontal and lies behind the fundus of the gall-bladder, passing backward and to the right from the pylorus. The second part runs vertically downward in front of the hilum of the right kidney, and into this part the pancreatic and bile ducts open. The third part runs horizontally to the left in front of the aorta and vena cava, while the fourth part ascends to the left side of the second lumbar vertebra, after which it bends sharply downward and forward to form the duodeno-jejunal flexure.
The jejunum forms the upper two—fifths of the rest of the small intestine; it, like the ileum, is thrown into numerous convolutions and is attached by the mesentery to the posterior abdominal wall. (See Conrou AND Snaous MEMBRANES.)
The ileum is the remaining three-fifths of the small intestine, though there is no absolute point at which the one ends and
" _Outline of liver
Great omentum (cut) Transverse mesocolon
ggggfguifum the other begins. Speaking broadly, the Tami, of “usury, jejunum occupies the upper and left part gland oblique of the abdomen below the subcostal musde plane (see ANATOMY: Superficial and
Artistic), the ileum the lower and right part. About 3 ft. from its termination a small pouch, known as M eckel’s diverticulum, is very occasionally found. At its termination the ileum opens into the large intestine at the ileo-caecal valve. The caecum is a blind sac occupying the right iliac fossa and extending down some two or three inches below the ileocaecal junction. From its posterior and left surface the uermiform aflrendix protrudes, and usually is directed upward and to the left, though it not infrequently hangs down into the true pelvis. This worm-like tube is blind at its end and is usually 3 or 4 in. long, though it has been seen as long as 10. in. Its internal opening into the caecum is about I in.
From A. Birmingham; Cunningham's Text-Book a] Anatomy.
FIG. L—The Abdominal Viscera in situ, as seen when the abdomen is laid open and the great omentum removed (drawn to scale from a photograph of a male body aged 56, hardened by formalin injections).
The ribs on the right side are indicated by Roman numerals; it will be observed that the eighth costal cartilage articulated with the sternum on both sides. The subcostal, intertnbercular, and right and left Poupart lines are drawn in black, and the mesial plane is indicated by a dotted ine. The intercostal muscles and part of the diaphragm have been removed, to show the liver and stomach extending up beneath the ribs. The stomach is moderately distended, and the intestines are particularly regular in their arrangement.
below that of the ileum. On transverse section it is seen to be composed of (r) an external muscular coat, (2) a submucous coat, (3) a mass of lymphoid tissue, which appears after birth, and (4) mucous membrane. In many cases its lumen is wholly or partly obliterated, though this is probably due to disease
usually tubular and is known as the pyloric canal. Before reaching this there is a bulging known as the pyloric vestibule (see D. ]. Cunningham, Tr. R. Soc. of Edinb. vol. xlv. pt. 1, N0. 2). The pylorus is an oval opening. averaging half an inch in its long axis but capable of considerable distension; it is formed by a special development of the circular muscle layer of the stomach, and during life is probably tightly closed. The mucous membrane of the stomach is thrown into pleats or rugae when the organ is not fully distended, while between these it has a mammillated appearance.
Superficial to the mucous coat is a sub-mucous, consisting of loose connective tissue, while superficial to this are three coats of unstriped muscle, the inner oblique, the middle circular and the
(see R. Berry and L. Lack, Journ. Anal. ('5' Phys. vol. x1. p. 247). Guarding the opening of the ileum into the caecum is the ileo-caecal value, which consists of two cusps projecting into the caecum; of these the upper forms a horizontal shelf, while the lower slopes up to it obliquely. Complete absence of the valve has been noticed, and in one such case the writer found that no abdominal inconvenience had been recorded during life. The caecum is usually completely covered by peritoneum, three special pouches of which are often found in its neighbourhood; of these the ileo-colic is just above the point of junction of the ileum and caecum, the ileocaecal just below that point, while the retro-caecal is behind the caecum. At birth the caecum is a cone, the apex of which is the appendix; it is bent upon itself to form a U, and sometimes this arrangement persists throughout life (see C. Toldt, “Die Formbildung d. menschl. Blinddarmes,” Sitz. der Wiener Akad. Bd. ciii.~ Abteil. 3, p. 41).
The ascending colon runs up from the caecum at the level of the ileo-caecal valve to the hepatic fiexure beneath and behind the right lobe of the liver; it is about 8 in. long and posteriorly is in contact with the abdominal wall and right kidney. It is covered by peritoneum except on its posterior surface (see fig. x). '
The transverse colon is variable in position, depending largely on the distension of the stomach, but usually corresponding to the subcostal plane (see ANATOMY: Superficial and Artistic). On the left side of the abdomen it ascends to the splenic flexure, which may make an impression on the spleen (see DUCTLESS GLANDs), and is bound to the diaphragm opposite the eleventh rib by a fold of peritoneum called the phrenico-colic ligament. The peritoneal relations of this part are discussed in the article on the coelom and serous membranes. !
The descending colon passes down in front of the left kidney and left side of the posterior abdominal wall to the crest of the ilium; it is about 6 in. long and is usually empty and contracted while the rest of the colon is distended with gas; its peritoneal relations are the same as those of the ascending colon, but it is more likely to be completely surrounded.
The iliac colon stretches from the crest of the ilium to the inner border of the psoas muscle, lying in the left iliac fossa, just above and parallel to Poupart’s ligament. Like the descending, it is usually uncovered by peritoneum on its posterior surface. It is about 6 in. in length.
The pelvic colon lies in the true pelvis and forms a loop, the two limbs of which are superior and inferior while the convexity reaches across tOIthe right side of the pelvis. In the foetus this loop occupies the right iliac fossa, but, as the caecum descends and enlarges and the pelvis widens, it is usually driven out of this region. The distal end of the loop turns sharply downward to reach the third piece of the sacrum, where it becomes the rectum. To this pelvic colon Sir F. Treves (Anatomy of the Intestinal Canal, London, 1885) has given the name of the omega loop. Formerly the iliac and pelvic colons were spoken of as the sigmoid flexure, but Treves and T. Jonnesco (Le Colon peloien Pendant la vie intra-utérine, Paris, 1892) have pointed out the inapplicability of the term, and to the latter author the modern description is due.
The rectum, according to modern ideas, begins in front of the third piece of the sacrum; formerly the last part of the Q (or omega) loop was described as its first part. It ends in a dilatation or rectal ampulla, which is in contact with the back of the prostate in the male and of the vagina in the female and is in front of the tip of the coccyx. The rectum is not straight, as its name would imply, but has a concavity forward corresponding to that of the sacrum and coccyx.
When viewed frorn in front three bends are usually seen, the upper and lower of which are sharply concave to the left, the middle one to the right. At the end of the pelvic colon the mesocolon ceases, and the rectum is then only covered by peritoneum at its sides and in front; lower down the lateral covering 15 gradually reflected off and then only the front is covered. About the junction of the middle and lower thirds of the tube the anterior peritoneal covering is also reflected off on to the bladder or vagina, forming the rccto-oesical pouch in the male and the pouch of Douglas in the female. This reflexion is usually about 3 in. above the anal aperture, but may be a good deal lower.
The anal canal is the termination of the alimentary tract, and runs downward and backward from the lower surface of the met?! ampulla between the levatores ani muscles. It is about an Inch long and its lateral walls are in contact, so that in section it appears as an antero-posterior slit (see J. Symington, Journ. Anat. and Phys. vol. 23, 1888).
Structure Of the Intestine—The intestine has four coats: sewn-‘5, muscular, submucous and mucous. The serous or
peritoneal coat has already been described wherever it is present. The muscular coat consists of unstriped fibres arranged in two layers, the outer longitudinal and the inner circular (see fig. 2). In the large intestine the longitudinal fibres, instead of being arranged evenly round the tube as they are in the small, are gathered into three longitudinal bands called taeniae (see fig. 1); by the contraction of these the large intestine is thrown into a series of sacculi or slight pouches. The taeniae in the caecum all lead to the vermiform appendix, and form a useful guide to this structure. In the rectum the three taeniae once more become evenly arranged over the whole surface of the bowel, but more thickly on the anterior and posterior parts. The circular layer is always thicker than the longitudinal; in the small intestine it decreases in thickness from the duodenum to the ileum, but in the large it gradually increases again,'_so_that it is thickest in the duodenum and rectum.
Circular muscular fibre.
The submucous coat is very strong and consists of loose areolar tissue in which the vessels break up.
The mucous coat is thick and vascular (see fig.2); it consists of an epithelial layer most internally'which forms the intestinal glands (see EPITHELIAL, ENDOTHELIAL AND GLANDULAR TISSUES). External to this is the basement membrane, outside which is a layer of retiform tissue, and this is separated from the submucous coat by a very thin layer of unstriped muscle called the muscularis mucosae. In the duodenum and jejunum the mucous membrane is thrown into a series of transverse pleats called oalvulae connioentes (see fig. 3); these begin about an inch from the pylorus and gradually fade away as the ileum is reached. About 4 in. from the pylorus the common bile and pancreatic ducts form a papilla, above which one of the valvulae conniventcs makes a hood and below which a vertical fold, the frenulum, runs downward. The surface of the mucous membrane of the whole of the small intestine has a velvety appearance, due to the presence of closely-set, minute, thread-like elevations called villi (see fig. 2). Throughout the whole length of the intestinal tract are minute masses of lymphoid tissue called solitary glands (see fig. 2); these are especially numerous in the caecum and appendix, while in the ileum they are collected into large oval patches, known as agminatod glands or Peyer’s patches, the long axes of which, from half an inch to 4 in. long, lie in the long axis of the bowel. They are always found in that part of the intestine which is farthest from the mesenteric attachment. In the interior of the rectum three shelf-like folds, one above the other, project into the cavity and correspond to the lateral concavities or kinks of the tube. They are not in the same line and the largest is usually on the right side. They are known as the plicac recti or valves of Houston. In the anal canal are four or five longitudinal folds called the columns of M orgagni. (For further details, see Quain’s Anatomy, London, 1896; Gray‘s Anatomy, London, 1905; Cunningham’s Analomy, Edinburgh, 1906.)
Embryology—The greater part of the alimentary canal is formed by the closing-in of the entoderm to make a longitudinal tube, ventral and parallel to the notochord. This tube is blind in front and behind (cephalad and caudad), but the middle part of its ventral wall is for some distance continuous with the wall of the yolk-sac, and this part of the canal, which at first opens into the yolk-sac by a very wide aperture, is galled the mid gul. The part in front of it, which lies dorsal to the heart, is the fore gut, while the part behind the aperture of the yolk-sac is the hind gut.
The pharynx, oesophagus, stomach and part of the duodenum are developed from the fore gut, a good deal of the colon and the
rectum from the hind gut, while the mid gut is responsible for the rest. The cephalic part of the fore gut forms the pharynx (q.'v.), and about the fourth week the stomach appears as a fusiform dilatation in the straight tube. Between the two the oesophagus gradually forms as the embryo elongates. The opening into the yolk-sac, which at first is very wide, gradually narrows, as the ventral abdominal walls close in, until in the adult the only indication of the connexion between the gut and the yolk~sac is the very rare presence (about 2%) of Meckel’s diverticulum already referred to. The stomach soon shows signs of the greater and lesser curvatures, the latter being ventral, but maintains its straight position. About the sixth week the caecum appears as a lateral diverticulum, and, until the third month, is of uniform calibre; after this period the terminal part ceases to grow at the same rate as the proximal, and so the vermiform appendix is formed. The mid gut forms a loop with its convexity toward the diminishing vilelline duct, or remains of the yolk'sac, and until the third month it protrudes into the umbilical cord. The greater curvature of the stomach grows more rapidly than the lesser, and the whole stomach turns over and becomes bent at right angles, so that what was its left surface becomes ventral. This turning over of the stomach throws the succeeding part of the intestine into a duodenal loop, which at first has a dorsal and ventral mesentery (see COELOM
AND Seaous MEMBRANES). The intestine now grows very rapidly and is thrown into a series of coils; the caecum ascends and passes to the right ventral to the duodenum, and presses it against the dorsal wall ~of the abdomen; then it descends toward its permanent position in the right iliac fossa.
From the ventral surface on the hinder (caudal) closed end of the intestinal tube the allanlois grows to form the placenta and bladder (see URINARY SYSTEM, REPRODUCTIVE SYSTEM and PLACENTA), and this region is the cloaca into which the alimentary, urinary and generative canals or ducts all open, but later two lateral folds appear which, by their union, divide the cloaca into a ventral and a dorsal part, the former being genito-urinary and the latter alimentary or intestinal. In this way the rectum or dorsal compartment is shut 05 from the genito—urinary. Later an ectodermal invagination at the hind end of the embryo develops and forms the anal canal; this is the Proclodaeum, and for some time it isseparated from the hind (caudal) end of the rectal part of the mesodaeum (or part of the intestinal canal formed from the mesoderm) by a membrane called the anal membrane. This is eventually absorbed and the digestive tract now communicates with the surface by the anus.
F. Wood Jones (British Medical Journal, 17th of December 1904) has given a somewhat different description of the development of the cloaca and anus, which better explains the various abnormalities met with in this region but requires further confirmation before it is generally accepted. For the development of the mouth, pharynx, lungs, liver and pancreas from the primitive alimentary canal, the reader is referred to the special articles OD'tllOSC structures. (For further details, see W. His, Anatomic menschlirher Embryonen (Leipzig, 1880-188 5); C. S. Minot’s Embryology (New York, 1897) ;and J. P. M‘Murrich, Develoflment of the Human Body (London, 1906). (F. G. P.)
Comparative Anatomy—The primitive condition of the vertebrate alimentary canal may be described as a straight, simple tube, consisting of an anterior portion, the slomoda-eum, formed by an ectodermal invagination, the mesenlcron, a long median portion lined by endoderm, and a short posterior portion, the proclodaeum, formed by ectodermal invagination. In the lower vertebrates the primitive tube subserved also the purpose of respiration, and traces of the double function remain in the adult structure of 'all vertebrates (see Mourn, PHARYNX). In fish, the pharynx, or branchial region, suddenly beecmes narrower, posterior to the gill-slits, to form the oesophagus; in higher animals the oesophagus, in the adult, is separated from the primitive pharyngeal region and lies dorsal to it. Probably, in the primitive vertebrata, the entire alimentary canal was lined with ciliated cells. Traces of this ciliation persist in many living forms. In the Ammocoete, the larval form of Pelromyzon (see CYCLOSTOMATA), the whole Canal is ciliated except the pharynx and the rectum; in the Dipnoi the epithelium of the stomach and the intestines is ciliated; in Selachli that of the posterior part of the gullet, and the spiral valve, is ciliated; extensive ciliation may occur in almost any region of the gut of the lower teleostomes, but in the higher forms (Teleoslei) it is generally absent. In the latter, however. and in higher groups of vertebrates, a peculiar striated border on the columnar cells lining the intestinal tract has been held to be a final trace of ancestral ciliation.
The alimentary canal may be conveniently described in three divisions, the oesophagus or gullet, the passage by which food reaches the stomach, the stomach, typically an expanded region in which the food remains for a considerable time and is mechanically pulped, mixed with mucus and certain digestive juices (see NUTRITION) and partly macerated, the intestinal tract or gut, extending from the distal end of the stomach to the cloaca or anus, in which the food is subjected to further digestive action, but which is above all the region in which absorption of the products of digestion takes place, the refuse material together with quantities of waste matter entering the gut from the blood and liver being gradually passed towards the anus for discharge from the body. “1,5
The oesophagus is essentially merely a passage, as straight as