THE ELASMOBRANCH FISHES 169 



The iliac artery arising? from the dorsal aorta in the pelvic region is larger 

 than tlie subclavian. The first branch of the iliac on the left side, the rectal, is 

 asjanmetrical and passes forward to supply the wall of the rectum (see r., figs. 

 155 and 157) . Before the iliac, as the femoral, passes through a foramen in the 

 pelvic girdle to supply the jielvic fin, it joins the posterior part of the lateral 

 artery (pi.) . 



ARTERIAL SUPPLY TO DEEPER STRUCTURES 



The third set of paired arteries arising from the dorsal aorta consists «of seg- 

 mental arteries {sg., fig. 157) . The first of these segmentals may arise from the 

 paired dorsal aorta (sg., fig. 152) throughout the pharyngeal region and per- 

 forate the deeper musculature around the spinal column. 



In the region between the subclavians and iliacs about thirty pairs of regu- 

 larly arranged segmental arteries leave the aorta. Each segmental sends a 

 branch dorsally around the spinal column supplying a median branch to the 

 spinal cord and lateral branches to the musculature, and is continued by a 

 superficial intercostal branch (ic.) which runs along the peritoneum bound- 

 ing the body cavity. These intercostals extend outward to supply the inter- 

 septal musculature and are often of great length. Occasionally, however, some 

 of these are lacking, and the interseptal spaces, especially in the region of the 

 mesonephros or kidney, may be supplied by neighboring arteries. 



The renals are the most ventral branches of the segmentals. They are more 

 irregular along the anterior prolongation of the kidney, but in the posterior 

 region where the kidney is enlarged they are regular in position and of large 

 size. 



The oviducal arteries in Heptanchus {od.a., fig. 157) arise from the third 

 pair of segmentals back of the subclavians. These arteries run posteriorly, and 

 at a])out the eighth segment behind the subclavians liecome tortuous in their 

 course ending in segment nine or ten. 



Caudal Aorta 



The dorsal aorta, as the caudal artery, traverses the haemal canal to the tip of 

 the tail giving off segmentals similar in general to those of the trunk. These 

 pass from, the caudal aorta laterally through interhaemal spaces and branch 

 into ventral and dorsal divisions; the ventral branches go to the ventral mus- 

 cles and the dorsal branches pass upward and around the body of the centrum. 

 From the dorsal part, spinal arteries are given off which enter the neural canal 

 to supply the spinal cord. 



