CHANGES IN THE OVUM. 79 



which were originally deposited upon the membrane. They contain 

 much oxalate of lime. 



Differences. 



Ruminants. 



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

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

 which 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 hippomanes^ are found in the allantoic 

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

 dense, smaller, and of a lighter color. 



Pig. 



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

 of ruminants, except that it is less sacculated, and shows at the extremity 

 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 possessing 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 hippomajies., 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 umbilical vesicle^ saccus intestinalis, or vesicula 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 oppo- 

 site 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 color, 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 

 umbilical 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 connected 



