24 WILLIAM F. ALLEN 



the last vertebra the ventral stem after receiving a communica- 

 tion from tlie dorsal stem, enters the haemal canal with the caudal 

 and the minor caudal arteries to form the beginning of the 

 longitudinal haemal lymphatic trunk. Near the last vertebra the 

 dorsal stem of the caudal lymphatic trunk receives two hypural 

 lymphatic vessels (figs. 4-7, Hyp.T.) coming from either side of 

 the superior hypural bone, which follow the course of their cor- 

 responding arteries, often nearly surrounding them, and each 

 collects a parallel network from the dorsal and posterior lateral, 

 surfaces of the superior hypural bone, which is continuous with a 

 similar network that is gathered by the posterior neural lymphatic 

 vessel. It should be noted, however, that no vein was seen col- 

 lecting the arterial network from the superior hypural bone, and 

 it may be that the so-called hypural lymphatic trunk receives 

 this network. Still, however, no connections were found between 

 the arterial network and the lymphatic network ; they ran parallel 

 to each other, and appeared to be two separate systems. On one 

 side of the superior hypural bone, but seldom on both, there is an 

 interlinking lymphatic canal (figs. 4, 6, and 7) connecting the 

 dorsal stem of the caudal trunk with either profundus portion 

 of the lateral lymphatic trunk or the posterior neural lympha- 

 tic trunk. 



Concerning the distribution and caudal ending of the dorsal, 

 ventral, and caudal lymphatic trunks in the tail region as des- 

 cribed by different authors there is great variation. In many 

 species the posterior portions of the dorsal and ventral subcu- 

 taneous trunks are large and important canals, and in place of the 

 small caudal lymphatic trunks between the hypural bones as was 

 described for Scorpienichthys there are large paired caudal sinu- 

 ses or hearts, which collect the lymph from the entire tail region 

 and discharge it directly into the caudal vein. 



In the Selachians, Parker (p. 721) found in Mustelus that the 

 posterior ventral cutaneous vein formed loops about the anal fin 

 and the cloaca, and posteriorly the lateral cutaneous veins were 

 said to anastomose with the dorsal cutaneous and the caudal 

 veins. Sappey observed that Squalus (pp. 38-9) possessed a dor- 

 sal and a ventral lymphatic trunk. The dorsal trunk was said 



