THE FCETUS. 



1027 



Fig. 563. 



branches are, finally, the result of the coalescing ; and these soon unite into a 

 single trunk, which accompanies the two arteries in the cord. On reaching the 

 umbilicus, this, the umbilical vein (Fig, 561), bends forward on the inner face of 

 the abdominal parietes, where it 

 is covered by the peritoneum, 

 and arrives at the liver, into 

 which it enters and opens di- 

 rectly into the vena portae ; the 

 junction of the two vessels 

 giving rise to a single canal, 

 from which proceed the sub- 

 lobular veins (Fig. 562). In 

 other animals than Solipeds, this 

 single vessel gives off a par- 

 ticular trunk of somewhat con- 

 siderable volume, which passes 

 directly to the posterior vena 

 cava, and forms what is named 

 the ductus venosus of Arantius 

 (Figs. 562, 563). 



Such are the umbilical 

 vessels, and it will be seen that they form a part of the circulatory system of 

 the young creature, which will be more completely studied hereafter. 



LIVER OF A LAMB AT BIRTH. 



, Posterior vena cava ; B, vena porta ; C, umbilical 

 vein; Z), anastomosis of the umbilical vein with the 

 vena portae. 



Differential Characters in the Annexes of the Fcetus of the other Animals. 



1. Rdminants. — Placenta. — The placental apparatus of the Cow is not uniformly spread 

 over the outer surface of the chorion, but is constituted by a variable number of vascular 

 bodies— about sixty on an average — disseminated here and there, and dovetailed by reciprocal 

 penetration of prominences and cavities, into analogous bodies on the inner surface of the 

 uterus, designated cotyledons. These are only thickened points of the mucous membrane, the 

 follicles of which are enormously enlarged. They exist, we have seen, before gestation ; but 

 observation demonstrates that they may be afterwards formed or entirely renewed, especially 

 in those cases in which accidental circumstances have rendered those present insufficient for 

 their oflSce. The largest are found in the body of the uterus ; in the cornua they are smaller 

 as they are nearer the extremity. Their form i& generally elliptical, and they are attached to 

 the uterine surface by a wide mucous peilicle; their surface is convex, and perforated by 

 numerous openings, into which the placental tufts pass. They have always a yellowish 

 colour, which, added to their external characteristics, gives them the appearance of a moril 

 mushroom. 



With regard to the placentie, they repeat, on the surface of the chorion, the disposition of 

 the cotyledons on the uterus. They are vascular, concave patches, closely embracing the 

 cotyledous, and showing on their surface a multitude of long ramifying papillae, which bury 

 themselves in the cotyledonal cavities. They are attached to the chorion by a very thick, 

 short, vascular pedicle. 



In the Sheep and Goat, the arrangement is the same, except that the cotyledons are 

 hollowed out in their centre, like a cup, and into this cavity the placentae are inserted (Fig. 565) 



Chorion. — The primary chorion disappears at the same time that the amnion is formed, and 

 it is completely replaced by the definitive chorion towards the twentieth day, in tlie foetus of 

 the Sheep. The general form of this sac is an exact repetition of that of the uterine cavity. 

 This membrane responds to the inner face of the uterus, in the iuterplacental points. These 

 points constitute the chorion (or decidua) serotina, and the part carrying the placentae is named 

 the chorion frondosum. The inner face of the chorion is united to the amnion and the allaatoia 

 by means of inter-annexial laminated tissue. 



Allantois. — Very diflerent from that of the Mare, and otherwise much less complicated, 

 the allantois of Ruminants is a very elongated cavity, the middle portion of which receives 

 the insertion of the urachus, and its extremities are prolonged into the two cornua of the 



