Subcutaneous Vessels in Tail of Lepisosteus 51 



Eunning parallel with the caudal artery, but below in the haemal 

 canal, is the caudal vein (Figs. 1-7 and 9-19, C. V.). Although its 

 walls are much thinner, yet, when expanded, its diameter is much 

 greater than the arterial trunk, and below the tenth from the last 

 vertebra it resembles a sinus. At this point it receives a large neural 

 vein from above and the two caudal sinuses from above and the rear. 

 The entrances of the latter are guarded by a pair of semi-lunar valves. 

 Tracing the caudal vein posteriorly, it was found to leave the hgeraal 

 canal at the seventh or eighth htemal spine of the tail (counting ventro- 

 dorsad), in company with, but ventral to, the left caudal sinus. Occa- 

 sionally, however, the vein accompanies the right caudal sinus; in which 

 case the left caudal vein is the main stem, and drains the tin. At 

 first, the caudal vein is a more superficial vessel than either the caudal 

 artery or the so-called caudal subcutaneous trunk, for it passes caudad 

 between the superficial and the deep muscles of the fin. Upon reaching 

 the basal canal of the tail, between the third or fourth and the fourth 

 or fifth rays (counting dorso-ventrad), it immediately makes a curve 

 at right angles to pass ventrad through this canal in front of the caudal 

 subcutaneous trunk and either lateral to the caudal artery or between 

 it and the caudal trunk. From each ray it receives two branches that 

 traverse the upper and lower surfaces of the ray and collect a capillary 

 network from the fin membrane. This vein usually lies betw^een the 

 caudal ray artery and the caudal ray subcutaneous canal, but frequently, 

 toward the base of the ray, it runs laterad with the artery, immediately 

 proxamad of the caudal ray canal. 



Fig. 23 is from a posterior view of a transverse microscopic section 

 taken through the h^mal canal of a 90 mm. L. osseus. The caudal 

 artery (C. A.) presents no special peculiarities. It is composed of a 

 muscular layer, which is lined internally with an endothelial layer, and 

 is filled with corpuscles, mostly red. The caudal vein (C. V.), on the 

 contrary, is devoid of all muscular elements, and in specimens of this 

 size is composed solely of a layer of endothelium, containing very few 

 corpuscles. Both the artery and vein are supported in the hsemal canal 

 by a spongy connective tissue, and are accompanied by two additional 

 longitudinal trunks, which will be described later on. 



In Fig. 11 Hopkins- figures the caudal vein of Amia (:=Amiatus) 

 as ending under the eighth from the last vertebra and here receiving 



^Hopkins, G. S. "The Lymphatics and Enteric Epithelium of Amia calva," 

 The WiUlrj- Quarter-Ccntvnj Book. Ithaca, N. Y., pp. .307-38.5, 1893. 



