214 



THE ELASMOBRANCH FISHES 



propterygium joins the lateral abdominal vein independent of the brachial 

 (Raia erinacea, fig. 194b) . In Raja nasuta two independent brachial branches 

 join the lateral vein. 



In Heptmichus it was seen that the subscapular vein (s.sc.v., fig. 187) is an 

 important tributary of the lateral abdominal, emptying, in common with the 

 brachial as a brachioscapular vessel, blood from the pectoral girdle and from 

 the lateral cutaneous vessel. In Mustelus kcnlei a short subscapular trunk 

 joins the brachial but all blood from the lateral cutaneous reaches the heart 



through the postcardinal. Squalus 

 sucklii is of interest as a type 

 which actually bridges these two 

 extremes. In it the lateral abdom- 

 inal {l.a.v., fig. 197), just before 

 entering the duct of Cuvier, re- 

 ceives the brachioscapular trunk 

 which includes the subscapular 

 vein (s.sc.v.). Now the subscapu- 

 lar vein dorsally comes in contact 

 with, and has an opening into, 

 the postcardinal sinus (p.c.s.). 

 The lateral cutaneous vein (Lev.) 

 empties into the subscapular near 

 the union of the subscapular with 

 the postcardinal sinus, so that the 

 blood from the lateral cutaneous 



Fig. 197. Diagram of relations of postcardinal 

 to lateral abdominal system, Squalus sucTclii. 



'br.v., brachial vein; h.s.c, brachioscapular; 

 co.v., coracoid vein ; d.c, duct of Cuvier ; l.a.v., 

 lateral abdominal vein; l.c.v., lateral cutaneous 

 vein; p.c.s., postcardinal sinus; s.cl.v., subclavian 

 vein; s.sc.v., subscapular. 



vein after entering the subscapular may pass dorsally into the postcardinal 

 sinus or ventrally into the lateral abdominal vein. In other words, if the sub- 

 scapular vein of Squalus sucklii had no connection with the postcardinal sinus, 

 Squalus would be in all essentials of the type of Heptanchus. If, however, that 

 segment of the subscapular between the entrance of the lateral cutaneous 

 (Lev., fig. 197) and the brachial vein (hr.v.) were dropped out, then the 

 lateral cutaneous would be independent of the lateral abdominal system and 

 the type would be like that of Mustelus or Scyllium. 



After receiving the brachioscapular trunk (brachial and subscapular), the 

 lateral abdominal vein as the subclavian (s.cl.v.) turns sharply upward in the 

 pericardio-peritoneal wall and across the scapular cartilage to empty into the 

 duct of Cuvier (d.c.) as in Heptanchus. 



The history of the lateral abdominal system is of interest. In origin it is one 

 of the earliest of the systems to appear. Furthermore it occupies a position 

 which would have been of particular value had a lateral fin-fold been present, 

 for such a vessel would have drained this fold directly as it does those parts 

 of the fold which remain, that is, the paired fins. 



The lateral abdominal vein has often been considered in relation to the 

 ventral abdominal vein of the amphibians which in its anterior and posterior 

 sections drains the paired appendages, but in the middle region is a single 



