1918] Daniel: The Subclavian Vein in Elasmohranch Fishes 483 



Discussion 



From the work of Parker and 'Donoglme it is clear that the sub- 

 clavian vein of Elasmobranchs enters the duet of Cuvier and not the 

 postcardinal sinus as stated by Rabl (1892). But the character of 

 the blood which it receives depends in great part on the subscapular 

 vein and its relations. 



I am of the opinion that the lateral abdominal, as is postulated by 

 the lateral fin-fold theory, should be regarded as the main vessel in 

 relation to the paired fins. As such it should receive the veins of the 

 paired fins and also of their girdles. This case is realized in Hep- 

 tanchus where anteriorly the lateral abdominal receives the brachial 

 from the fin and the subscapular and coracoid veins from the girdle. 

 Furthermore the subscapular and the coracoid increase the importance 

 of the lateral abdominal by receiving all of the blood from the lateral 

 and ventral cutaneous veins. 



The finding of Parker for Musielus and O 'Donoghue for Scyllium, 

 that the subscapular with its lateral cutaneous tributary empties into 

 the postcardinal sinus doubtless represents the most usual condition ; 

 but that this is not universal, and that it is brought about secondarily 

 has, I think, been shown in the present paper. Whether the post- 

 cardinal receive any of the blood from the lateral cutaneous depends 

 upon the subscapular vein. If the subscapular is unbroken and un- 

 connected with the postcardinal, as in Heptanchus (fig. 1), all of its 

 blood reaches the heart by way of the lateral abdominal and sub- 

 clavian. In Squalus (fig. 2) where the subscapular vessel, although 

 continuous, is secondarily connected to the postcardinal there is a 

 transition from the more generalized heptanchid type to a more 

 specialized type like that of Miisteliis in which the subscapular is 

 divided into two parts, a distal sinusoid surounding the tip of the 

 scapular cartilage, and a proximal more or less abbreviated portion. 

 In this more specialized case, blood entering the distal part from the 

 lateral cutaneous vein has but one course open to the heart and that 

 through the postcardinal sinus. 



