THE ABDOMEN. 253 



laxative effect, and serves to remove from tlie alimentary 

 canal of the newly born animal the meconium or inspissated 

 biliary matter which has accumulated in the intestines 

 while the animal was in the uterus, in consequence of the 

 large supply of blood received by the liver during that 

 period. Where this precaution is neglected, the meconium 

 sometimes collects in large quantities of pellets, like sheep 

 dung in the rectum, causing obstinate constipation. 



The dissector may be fortunate enough to obtain a preg- 

 ^nant animal for dissection ; he will then be enabled to 

 study the FCETAL APPENDAGES. By cutting through 

 the walls of the uterus, he will expose the chorion lying 

 in immediate contact with the uterine mucous membrane 

 over its whole surface. It consists of an intricate network 

 of blood-vessels arranged in a ^^lexiform manner to come 

 in apposition with the vascular layer of the uterine mucous 

 membrane. While in these vessels, being separated from 

 the blood of the dam only by layers of epithelial cells and 

 of basement membrane, the blood of the foetus is enabled 

 to exchange carbonic anhydride for oxygen, sufficient in 

 quantity to support his torpid life, for he moves but little, 

 and his temperature is maintained by that of his dam in 

 whose body he lies ; thus two of the demands for oxygen 

 in the blood which obtain after birth are absent in the 

 foetus, and his life consists more in active addition to 

 existing structures, growth, than in disintegration of tissue 

 with substitution of fresh matter, such as obtains in the 

 adult. Blood from the internal iliac branch of the posterior 

 aorta of the foetus passes through the umbilical arteries. 

 These vessels, which in the adult become impervious, de- 

 generating into the round ligaments of the Madder, after 

 becoming attached to their respective sides of the bladder 

 gain the umbilical opening ; here they unite and form one 

 vessel, which runs outside the body of the foetus to the 

 chorion through the umbilical cord. The veins of the 

 chorion unite and reunite to at last form two vessels which 

 pass along the umbilical cord, and on gaining the umbili- 

 cus unite to form the umbilical vein, which runs in a- 

 forward direction along the floor of the belly between the 

 peritoneal folds, forming the falciform ligament of the liver 

 to which organ it runs without (in the colt) having any direct 

 communication with the posterior vena cava through the 

 ductus venosus as found in many other animals. It passes 



