TEE FCETU8. 



1025 



6. The Umbilical Cord (Figs. 556, 557). 



The c&rd is formed by the vessels which, in the foetus, caiTy the blood to the 

 envelopes, and chiefly to the placenta. It is divided into two portions — an 

 amniotir, 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 aUantoid portion (Fig. 557, B) — 

 much shorter and less twisted, is enveloped by 

 the sheatli that continues the two layers of the 

 allantois, and is inserted into the superior wall 

 of the chorion, between the two cornua.^ 



Three vessels compose the cord — two arteries 

 and a I'ein ; these are covered by a layer of 

 embryonic tissue — the fielatine 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 ramitications. These 

 arteries run parallel to the median plane of 

 the body of the foetus, to the umbilicus ; they 

 are perpendicular at the infundibuluin, which 

 proves that the allantois undergoes a twist in 

 the early period of development. The amniotir 

 divisions of these arteries are few, and extremely 

 flexuous ; they are included between the allantoid 

 layer and the amniotic membrane, within which 

 they may be seen projecting. 



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 are very prominent. By their anastomoses 

 they form a very rich network, from which proceed the capillary twigs that 

 enter the villosities of the placenta. Observation demonstrates that these twigs 

 do not communicate with the maternal vessels, and that they are continued by 

 venous radicles, the origin of the vessel now to be described. 



The Umbilical Vein commences by these capillary radicles of the placental 

 villi, which unite between the chorion and amnion to form a network of more 

 voluminous divisions and complexity than that of the arteries. Two principal 



' Goubaux has remarked that the relations between these two portions are not constant. 

 In a six months' foetus, tlie aranintic part measured 40 m., and the allantoid part '24 m. In a 

 foetus of ten months, the first was 30 m. long, and the second '20 m. 



* The walls of the umbilical arti ry are very rich in muscular iibres, which are lon^itudiniil 

 and transversal, but are irregularly distributed. There is no internal elastic tunic in any of tho 

 branches external to the umbilicus. 



PORTION OF ONE OF THE FCETAL 

 VILLI, ABOUT TO FORM PART OF 

 THE ILACENTA (HIGHLY MAGNI- 

 FIED). 



a, n. Its cell covering; 6, h, h, its 

 looped vessels; c, c, its basis of con- 

 nective tissue. 



