81 OBSTETRICAL PHYSIOLOGY. 



Differences. 



BiUminants. 



In Ruminants the allantois is different to that of the Mare, being less 

 complex. It represents a very elongated cavity, the middle portion of 

 Mrhich is not extensive, and receives the insertion of the urachus ; while 

 its extremities, which are unequal, are prolonged into the cornua of the 

 chorion, where they are attached by a small ligament. This sac is in 

 reality an expansion of the urachus ; it is always thrown back on one 

 of the sides of the amnion. In the completely developed foetus, 

 even at birth, the allantois still communicates directly with the bladder 

 by means of the urachus. Frequently in the Sheep this membrane 

 exceeds the chorion, and in the case of twin embryos, although the two 

 chorial sacs unite by one of their cornua, there is only a simple external 

 union between the two allantoid membranes, the cavities remaining 

 isolated. 



Laminated deposits, like the Jdppomanes, are found in the allantoic 

 fluid of Euminants, though not very frequently. These deposits are less 

 dense, smaller, and of a lighter colour. 



Pig. 

 In the Pig the allantois does not offer any marked difference from that 

 of Euminants, except that it is less sacculated, and shows at the ex- 

 tremity of each cornua a small portion projecting beyond the chorion, 

 which it seems to pierce, while it is strangled by a kind of rings formed 

 by that envelope. In the gelatinous tissue connecting the allantois to 

 the chorion are numerous small, white, spherical bodies, each possess- 

 ing a distinct capsule ; they are composed of multitudes of circular 

 cells, the size of lymph corpuscles, and quantities of granular particles 

 — being, in fact, histologically the same as the hij^j^onianes , with which 

 they are probably homologous. 



Bitch and Cat. 

 In the Bitch and Cat it is disposed in the same fashion as in Solipeds. 

 Its external layer adheres less closely to the chorion, except at the part 

 corresponding to the placenta, where it is more intimately united. 



Umbilical Vesicle. 



The umhilical vesicle, saccus intestinalis, or vcsicida alba, is a small 

 fusiform or pyriform pouch lodged in the infundibulum at the extremity 

 of the umbilical cord. Its fundus adheres to the chorion, while the 

 opposite end is prolonged to a certain length in the substance of the 

 cord, being even continued, in the very young foetus, to the abdominal 

 cavity by a narrow canal that communicates with the terminal portion 

 of the small intestine. 



This pouch has a red colour, due to its great vascularity, its walls 

 receiving a special vessel from the anterior mesenteric artery ; the ter- 

 minations of this vessel give rise to a corresponding vein that terminates 

 in the vena portae. These are the two omphalo-mesenteric vessels. The 

 umbihcal vesicle in Solipeds is constantly present as a normal formation 

 in the earlier months of foetal development, being formed from the 

 extra-foetal portion of the internal layer of the blastoderm. It is con- 

 nected with the intestinal canal of the foetus ; being in reality the 

 vitellus surrounded by the blastoderm upon which the embryo is first 

 formed ; and it bears a perfect analogy to the yolk of the egg, except 

 that it is not ultimately enclosed within the foetal abdomen. It is a. 



