THE AETEEIES 321 



f. The lumbar arteries are small median arteries, 



arising from the dorsal surface of th^ aorta, and 

 dividing into right and left branches supplying 

 the body- walls. 



g. The median sacral artery is a small vessel arising 



from the dorsal surface of the aorta, shortly before 

 its division, and running along the ventral surface 

 of the sacrum to the tail. It is to be regarded as 

 the posterior continuation of the aorta. 



h. The common iliac arteries, formed by the bifurca- 

 tion of the aorta, run backwards and outwards to 

 the hind-Umbs, along which they are continued 

 as the femoral arteries. In the abdomen each 

 gives off the following branches. 



i. The ilio-lumbar artery runs outwards along the 



posterior part of the dorsal wall of the 



abdomen, 

 ii. The internal iliac artery runs backwards along 



the dorsal wall of the pelvic cavity, 

 iii. The vesical artery is a small branch which 



runs backwards to the bladder. In the female 



it also supplies the uterus. 



4. The pulmonary artery has already been described 

 (p. 313). 



Follow the branches of the pulmonary artery into the lungs. 



D. Dissection of the Heart. 



Cut across the great vessels, about half an inch from the 

 heart. Bemove the heart, and pin it down under water with 

 the dorsal surface upwa/rds, passing the pins through the ven- 

 tricles and the arch of the aorta. Clean carefully the roots 

 of the several vessels. 



1. The auricles. 



Cut a/way the outer walls of both auricles so as to expose 

 their cavities. Wash out the contained blood. 



