192 THE ELASMOBRANCH FISHES 



The subclavian is continued ventrally along the coracoid segment of the 

 girdle by the coracoid artery {co.a., fig. 166a), which at the ventral part of 

 the girdle gives off posteriorly the anterior lateral artery (a.l.) which is the 

 anterior part of the lateral (abdominal) artery. This artery, as in Heptanchus, 

 runs under the walls of the lateral abdominal vein and continues posteriorly 

 past the iliac arter3^ As the coracoid is followed forward and inward it is seen 

 to meet its fellow from the opposite side in the midventral line and to give off 

 the posterior coronary (cr.p., figs. 153 and 169) to the heart. By the union of 

 right and left coracoids a median stem is formed. This stem joins the commis- 

 surals from the ventral efferent-collector loops. 



The iliacs have the same form and take the same direction as the renal ar- 

 teries but their terminal parts extend into the pelvic fins as the femoral ar- 

 teries. The iliac artery arises from the posterior part of the lateral (abdomi- 

 nal) artery (p.L, figs. 157 and /.m., 177b) . In the rays Parker has figured renal 

 arteries arising from the iliacs. These renal arteries apparently are not com- 

 parable to the rectal artery in Heptanchus. A rectal (hypogastric) artery in 

 Squalus sucMii {r., fig. 179) may arise from the femoral or from the iliac. As 

 in Heptanchus maculatus it runs to the digestive tract and anastomoses with 

 the posterior intestinal. The iliac is continued to the pelvic fin as the femoral 

 which distributes smaller arteries both to the dorsal and the ventral sides of 

 the fin. 



SEGMENTALS 



For convenience the segmentals may be divided into three groups. One group 

 consists of the musculospinal arteries (fig. 170a), anterior to the subclavian 

 arteries; the second group is situated between the subclavians and the iliacs; 

 and the third set is posterior to the iliacs in the region of the tail. 



The musculospinal arteries are usually paired, but sometimes they are more 

 or less irregularly arranged. The first pair of these in Heterodontus passes 

 upward and around the spinal column and through small canals in the poste- 

 rior walls of the cranium (see p. 54, fig. 61) . The intercostal branches of these 

 segmentals may divide just over the pharynx as in Zygaena (fig. 170b), or 

 they may be regular as in Acanthias (fig. 170a) . In Baja the myelonal artery 

 (ml., fig. 170c) supplies the spinal cord. 



A trunk segmental sends a large vertebromuscular branch dorsally around 

 the vertebra and up the dorsal septum to the middorsal line. As seen in a trans- 

 verse section of Squaliis sucklii {d.vm., fig. 180) this artery gives rise to a 

 number of branches, the most dorsal of which ( elms. ) passes upward along the 

 myoseptum to supply the musculature of the dorsomedian bundle. In the re- 

 gion of the dorsal fins large branches of this artery extend into the fins. The 

 next branch given off, the vertebrospinal artery, passes mediad through the 

 neural arch to supply the spinal cord. Inside of the neural canal this artery 

 divides into a dorsal branch, the ramus dorsalis {Acanthias, fig. 181, d.r.), and 

 a ventral branch, the ramus ventralis {v.r.). The smaller ramus dorsalis forms 

 the tractus arteriosus lateralis (tr.l.), which passes both backward and for- 



