54 • William F. Allen 



or both surfaces of the rays, j^arallel with, but usually distal to, the 

 corresponding arteries. 



With the Selachians in addition to the subcutaneous vessels described 

 by Sappey {op cit., p. 39) for the dorsal fin, Parker*^ (p. 720) and 

 Mayer {op. cit., pp. 333-5) find a deeper vein, which is in connection 

 with this system and helps drain this region. By Mayer it has been 

 styled as the vena profunda (PI. XVI, Figs. 31, 23 and 24, v. prof.), 

 and, in brief, Mayer sets forth the union of the so-called subcutaneous 

 veins with the profundus as follows : The dorsal subcutaneous vein, at the 

 insertion of the dorsal fin separates into two vence circulares, which 

 encircle the fin and collect subcutaneous branches from it. Posteriorly 

 they reunite at the base of the fin in a reservoir. This reservoir also 

 receives one or two vena postica (V. P.), which travel along the distal 

 edge of the fin cartilage and collect the blood from the inner parts of 

 the fin. The vena profunda, in addition to collecting numerous 

 branches from the fin muscles, which run parallel to the corresponding 

 subcutaneous branches, communicates directly with the above mentioned 

 subcutaneous reservoir at the posterior insertion of the fin, and eventu- 

 ally passes along the sheath that separates the great lateral muscles, to 

 terminate in the caudal vein, or, acording to Parker, with Mustelus 

 empties into the left renal portal vein. • 



If in Lepisosteus we had the dorsal fin vein fusing with the dorsal 

 subcutaneous trunk at the posterior end of the dorsal fin, or, better still, 

 if the dorsal subcutaneous trunk (Figs. 1 and 2, D. T.), instead of 

 passing through the basal canal of the fin, had formed two circular 

 canals around the base of it, and had joined the dorsal fin vein in a 

 sinus at the posterior base of the fin, we would have a condition of 

 affairs almost identical with that found in the Selachians. Can it not 

 therefore be possible that farther back in the phylogeny, or possibly in 

 the embryo of Lepisosteus, the dorsal fin vein had such a comunication, 

 and that as specialization advanced the subcutaneous vessels became 

 more and more separated from the deep, and with this differentiation 

 a change in function occurred? In such a case the vena profunda and 

 the vena postica of the Selachians would be homologous to the dorsal 

 fin vein and its branches of Lepisosteus. 



*Parker, T. J. "< )n the Blood- Vessels of Mustelus antarcticus : a Contribu- 

 tion to the Morpliology of the Vascular System in the Vertebrata," Phil. 

 Trans., pp. G85-732, 1886. 



