xii VASCULAR SYSTEM 319 



the hyoidean sinus of its side, and, after receiving the nutrient 

 veins from the holobranchs of the first four branchial arches, opens 

 into the corresponding Cuvierian duct. 



The venous blood from the heart itself is collected into two 

 coronary veins, which open into the sinus venosus. 



In addition to the more important veins already described, 

 there is also a series of median and lateral cutaneous veins com- 

 municating at different points with certain of the more deeply 

 seated veins (Fig. 187). 



Characteristic features in the venous system of Mustdus, as 

 also of Elasmobranchs in general, are the development of trans- 

 verse connexions between certain of the principal paired veins, 

 and the tendency of many of the main veins to enlarge into more 

 or less irregularly -shaped sinuses. 



In its broad outlines the venous system of the Teleostomi 

 agrees with that of Elasmobranchs, but is nevertheless character- 

 ised by several more or less important modifications, while at 

 the same time exhibiting many differences in minor details. 



A renal portal system is usually present, but is singularly 

 variable in the source of its tributary veins, even in closely allied 

 forms. 1 In the Sturgeon (Acipenser) and in some Teleosts, as in 

 the Siluroid, Amiurus catus, it resembles that of Elasmobranchs. 

 In other Teleosts, on the contrary, the renal portal system presents 

 various grades of degeneration, or, possibly, of imperfect evolution, 

 as will be seen from the following illustrations of its condition 

 in different genera. 



In Amiurus the caudal vein, after giving off right and left 

 renal portal veins to the renal capillaries, emerges from the ventral 

 surface of the kidneys, and is then continued forwards between 

 the gonads, the veins from which it receives, as the radicle of the 

 hepatic portal vein. 



In the Eel (Anguilla vulgaris) the caudal vein (Pig. 188) 

 traverses the fused hinder portions of the kidneys, receiving 

 several segmental veins from the body-wall and also giving off 

 from each side numerous renal portal branches. More anteriorly, 

 where the two kidneys become distinct, the caudal vein also 

 divides into two renal portal veins and, as each vein extends 



1 Jourdain, Ann. Sci. Nat. (4), xii. 1859, p. 321 ; M'Kenzie, Reprint from the 

 Proc. Canadian Institute (N.S.) ii. 1884, p. 428. For references to Hyrtl and 

 other writers, see Jourdain, op. cit. 



