400 



J»ISEA,SES OF BLOOD-VESSELS. 



to recall the anatomical formation of the umbilical region in the new- 

 born animal. 



At birth the umbilical cord is represented by a cylindrical mass, 

 sm-rounded by the terminal portion of the amnion. It enters the 

 abdomen through a circular perforation in the abdominal wall known 

 as the umbilical ring. This ring may be divided into two parts, one 

 deeply seated, the fibro-aponeurotic ring, consisting of an aperture in 



Fig. 183. — rnsition of the abdominal \iscera in a new-born annnal : Ei/, rumen; 

 E, epiploon; Egr, left kidney; Ig, small intestine; C, abomasum ; U, ureter; 

 (), uraolius ; E, rectum. Umbilical cord: Yo, Umbilical vein; Aa, allantoid 

 arteries; \a, allantoid veins ; 0, tlie urachus. 



the white line ; the other the superficial or cutaneous ring, formed 

 by the skin, which is wrinkled all round it, and constitutes a kind of 

 sleeve about an inch in length. This cutaneous sleeve is continuous 

 with the amniotic tissues. The entire umbilical cord is therefore 

 enveloped in an amniotic-cutaneous sheath. 



It is composed of four principal structures — the umbilical arteries, 

 the umbilical vein, the urachus, and the interstitial mucous tissue. 



The umbilical arteries and vein consist of two parts — the extra-foetal 

 part, which co-operates in forming the cord, and the iijtra-f octal part. 



