. The comparative anatomy of the domesticated animals. Veterinary anatomy. 900 EMBRYOLOGY. villi. The fusion of these two systems has never been observed, and all the interchanges between the female and its young take place through the capillaries by osmotic force only. 6. The Umbilical Cord. The cord is formed by the vessels which, in the foetus, carry the blood to the enveloijes, and chiefly to the placenta. It is divided into two portions: an amniotic, the longest, which is always twisted on itself like a cord, and covered externally by the amnion that is prolonged on its surface, to be con
. The comparative anatomy of the domesticated animals. Veterinary anatomy. 900 EMBRYOLOGY. villi. The fusion of these two systems has never been observed, and all the interchanges between the female and its young take place through the capillaries by osmotic force only. 6. The Umbilical Cord. The cord is formed by the vessels which, in the foetus, carry the blood to the enveloijes, and chiefly to the placenta. It is divided into two portions: an amniotic, the longest, which is always twisted on itself like a cord, and covered externally by the amnion that is prolonged on its surface, to be continued with the skin around the umbilicus ; the other, the allantoid portion (Fig. 425, b), much shorter and less twisted, is enveloped by the sheath that continues the two laminse of the allautois, and is inserted into the supe- rior wall of the chorion, between the two cornua. Three vessels compose the cord: two arteries and a vein; these are covered by a layer of embryonic tissue, the gelatine of Wharton, which makes them appear much larger than they really are. The Umbilical Arteries arise from the internal iliac, and pass along the sides of the bladder; escaping by the umbilicus, they arrive at the terminal extremity of the amniotic portion of the cord, and giving off some branches to the amnion, they are continued to the extremity of the allantoid portion, where they end in an expansion of placental ramifications. The amniotic divisions of these arteries are few, and extremely flexuous; they are in- cluded between the allantoid layer and the amniotic membrane, within which they may be seen. The placental or chorial divisions, infinitely larger and more numerous, leave the end of the cord, and pass in every direction between the chorion and external lamina of the allantois, beneath which they project. By their anastomoses they form a very rich network, from which proceed the capillary twigs that enter tho villosities of the placenta. Observation demonstrates that these twi
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