8 WILLIAM F. ALLEN 



The iniiioi- fork of the caudal vein (figs. 3, 6, and 9, R.C.V.) 

 curves u]) around the right posterior side of the last vertebra in 

 front of the main stem of the caudal artery. When the median 

 line is reached, it usually divides; one branch passes laterad to the 

 periphery, and the other goes caudad a short distance between 

 the superficial and deep muscles of the caudal fin. In one dis- 

 section the minor fork of the caudal vein equaled the major fork 

 in length and in caliber. It continued caudad to the caudal fin, 

 where it })enetrated the ventral basal canal of the caudal fin, and 

 collected the blood from that half of the fin; while the blood from 

 the dorsal half of the fin was collected by the other or main fork 

 of the caudal vein. 



The main fork of the caudal vein or the caudal vein proper 

 (figs. 4-5, C.V., and figs. 3 and 9, L.C.V.) passes up the opposite 

 and usually the left posterior side of the last vertebra to the me- 

 dian line; where it receives the posterior neural vein (figs. 4 and 5, 

 P.Neu.V.), which in curving around to the dorsal side of the 

 superior hypural bone crosses directly mesad of the posterior 

 portion of the lateral trunk, to eventually follow up the left side 

 of the last neural spines. Meanwhile the main stem continues 

 caudad between the fascia or superficial muscles and the deep 

 muscles of the caudal fin. In its course between these muscles 

 it runs parallel with and mesad to the caudal fin nerve, and re- 

 ceives branches from these muscles. At the base of the tail this 

 vein takes a position quite close to the periphery, in fact, it trav- 

 els for some little distance directly mesad of the posterior por- 

 tion of the lateral lymphatic trunk, but never communicates 

 with the same. It then bends mesad to enter the basal canal of 

 the caudal fin, where it soon separates into the dorsal and ven- 

 trar caudal fin veins (figs. 4-6, and 11, C.F.V/ and C.F.V."). 

 In Scorpsenichthys the bifurcation of the main trunk of the caudal 

 vein occurs usually anterior to that of the caudal artery, nerve, or 

 the caudal lymphatic trunk, and for the most part the caudal fin 

 veins lie anterior to the other vessels in the basal canal of the fin. 

 In the Phancrodon embryo (fig. 11) the caudal artery forked at 

 the base of the tail before the caudal vein did, and the caudal 

 fin veins were posterior in position to the caudal fin arteries in the 



