I02 OBSTETRICAL PHYSIOLOGY. 



The rectum arises from the posterior intestine, and is developed like 

 the other portions. 



With regard to the anus, there is observed towards the caudal extrem- 

 ity of the foetus a depression analagous to the buccal cul-de sac. This 

 becomes deeper, and joins the rectum and genito-urinary organs ; later, 

 it separates from the last, and then belongs exclusively to the alimentary 

 canal. 



The ANNEXES OF THE ALIMENTARY CANAL are the salivary glands, teeth, 

 liver, pancreas, and spleen. The salivary glands are developed in a solid 

 cellular tubercle, which is connected with the epithelium at the upper 

 part of the digestive apparatus. With the growth of this tubercle, it is 

 converted into a series of cavities having the form of glandular culs-de-sac. 

 The submaxillary gland appears first, and it is entire in a foetus of only 

 twelve lines in length ; the parotid gland is the last formed. 



The teeth are developed in the interior of a cavity called the "dental 

 follicle " or "sac," by means of the elements of three germs correspond- 

 ing to the anatomical constituents of the teeth — enamel, ivory, and 

 cementum. The follicle is an oval cavity whose wall comprises two 

 layers : an external fibrous sac, and an internal gelatinous lining, at the 

 bottom of which is the ivory p nip or germ. This is a prominence detached 

 from the bottom of the sac, and has exactly the shape of the tooth. It 

 is composed of a mass of delicate cellular tissue provided with vessels 

 and nerves, and on the surface a layer of elongated cells. At the sum- 

 mit of the follicle, facing this pulp, is the enamel pulp, which fits accu- 

 rately on the dental pulp like a cap. This is made up of a small quantity 

 of mucous cellular tissue, covered by a layer of cylindrical cells connected 

 with the buccal epithelium by the gnberfiacnlnm dentis. The cement orgati 

 manifestly exists in the foal, being found at the base of the ivory germ, 

 though it disappears quickly after having performed its function. It is 

 unnecessary in this place to enter into a consideration of the develop- 

 ment of the teeth. 



The liver commences to be formed at an early period in all animals, 

 appearing at the surface of the duodenum in the shape of one large tu- 

 bercle or two small ones, according to the number of lobes in the organ of 

 the adult. To these external tubercles, corresponding internal ones arise 

 from the intestinal epithelium ; the first increase and enclose the omphalo- 

 meseraic vein, while the second ramify in their interior and form the 

 biliary ducts. 



The liver grows rapidly, and when about one-third of the period of ges- 

 tation has elapsed, it nearly fills the abdominal cavity. At a later date 

 this increase is less marked, although when gestation is nearly terminated, 

 the gland is -proportionately more voluminous than in the adult. 



The pancreas, like the salivary glands, is first seen as a solid cellular 

 tubercle, which is subsequently hollowed out by ramescent cavities. 



The spleen is developed about the second month, on the great curvature 

 of the stomach ; it would appear to be formed at the same time as the 

 pancreas, in a band extending from the stomach to the duodenum ; but 

 it is separated from the pancreas and becomes attached to the stomach, 

 where its elements assume the character of splenic tissue. 



The Genito-urinary Organs. 



The genito-urinary organs are related to each other in their develop- 

 ment, and have some parts in common. Immediately after the formation 



