THE FCETUS. 



1027 



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 reachini; the 

 umbilicus, this, the umbiliml vein (Fig. 5G1), 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- 

 lolnilar veins (Fig. 562). In 

 other animals than Solipeds, this 

 single vessel gives off a par- 

 ticular trunk of somewhat con- 

 sideral>le 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. 



MVER OF A LAMB AT HIRTH. 



A Posterior vena cava ; B, vona portae ; C, umbilical 

 vein; D, anastomosis of the umbilical vein with the 

 vena portae. 



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



1. Ruminants. — Placenta. — The placental apparatus of the Cowls not uniformly spread 

 over the enter surface uf tiie chorion, hut is constituteil by a variable number of vascular 

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

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

 uterus, desi_'nated cotyledons. Tin se are only thickened ])oint8 of the mucous membrane, tlie 

 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 whicn accidental circumstances have rendered those present insufficient for 

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

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

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

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

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

 mushroom. 



With regard to the plarentse, they repeat, on the surf ice of the chorion, the disposition of 

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

 cotyledons, 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 t' at the cotyleduns are 

 hollowed out in their centre, like a cu|), and into this cavity the placentse are inserted (Fig. 505). 



Chorion. — The primary chorion disappears at the same time that the amnion is formeil, und 

 it is completely replaced by the definitive chorion towards the twentieth day, in tiie toetus of 

 the Sheep. The general form of this sac is an exact rcp.-tition of that of the uterine cavity. 

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

 points constitute the chorion (or deridua') sffvotina, and the part carrying the placentae is named 

 the chorion frondostnn The inner face «f the chorion is united to the amnion and the allantois 

 by means nf inter-annexial laminated tissue 



Allantois.— Xery different from that of the Mare, and otherwise much less complicated, 

 the allantois of Ruminants is a very elonj^ated cavity, the miildle portion of which receives 

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



