196 THE SALAMANDER 



Venous System. 



(i) Persistence of the post-cardinal veins, which may even in 



some cases retain their primitive connexions with Jacobson's 



veins, 

 (ii) The persistence of one of the vitelline veins of the embryo — 



the left — in a perfectly functional condition (see Rusconi's 



vein, p. 238). 

 (iii) The obvious derivation of the venous system of the head 



from Selachian-like sinuses, 

 (iv) The occasional absence of the middle portion of the post- 

 caval vein, and corresponding enlargement of one of the 



post-cardinals. 



As might be expected in an animal retaining so many primitive 

 features there is a considerable amount of individual variation to be 

 met with, and it is difficult to give a general account which will cover 

 all cases, but it is hoped that the following description, based mainly 

 on the dissection of specimens which have been injected with 

 Prussian blue (gelatine and liquid) injection masses, will enable all 

 the important vessels to be identified and followed. 



All vessels may be taken as paired unless definitely stated to be 

 otherwise. 



The vessels of the cranial and vertebral cavities, both arteries and 

 veins, are described at the end of the present main section under 

 'Vessels of the Brain'. 



3. Arterial Arches (PL XIV). 



The Salamander, after metamorphosis, normally retains all four 

 of the branchial arteries present in the larva, and rarely three only 

 are to be found. In the latter condition it is the 'third' arch which is 

 missing, its place being occupied by a strand of pigmented connec- 

 tive tissue bearing the same relation to the M. cephalo-dorso-sub- 

 pharyngeus and to the systemic arch as the artery does when present. 

 The other arches present are — naming from anterior to posterior — 

 (i) the carotid^ (2) the systemic^ and (4) the. pulmonary. 



The carotid — third visceral — arch (A. Ill) is not normally con- 

 nected with the systemic by a ductus Botalli, but in one specimen 

 such a connexion has been found on one side. It was exceedingly fine, 

 however, and only just visible under the dissecting microscope. 



The systemic — fourth visceral — arch (A. IV) is considerably larger 

 in diameter than the other arterial arches while it also receives the 

 blood leaving the heart by the 'third' arch. Its branches deliver blood 



