TRANSACTIONS OF SECTION D. 755 



anastomosis there with branches of the subclavian artery. This branch is of 

 greater size and importance in other reptilian forms and in birds. The dorsal 

 vessel supplies the whole of the head, its branches are numerous, and a number of 

 those which supply the outer aspect are grouped together at their origin into one 

 trunk. This dorsal vessel is in most cases continued directly backwards into the 

 aorta as in the young amphibian. 



The carotid arteries of the chelonian when examined closely are found to 

 resemble in position and distribution the vessels described in the lacertilian. A 

 ventral vessel extending to the tongue, but not constituting the whole supply of 

 ■that organ, runs forward upon the under surface of the throat. This ventral vessel 

 is a branch of the subclavian, but the apparent anomaly of its origin is explained 

 by the fact that the subclavian of the chelonian does not correspond to the sub- 

 clavian of the lacertilian, but to that branch of the ventral carotid which has 

 been alreadv described as passing outwards to the muscles of the shoulder. _ The 

 dorsal artery of the chelonian is similar in all its more important characteristics to 

 that of the lacertilian, and supplies the head externally and internally. 



The arrangement of the vessels of the crocodile resembles that of the chelo- 

 nian. The ventral vessel ' arteria collateratis colli' arises with the subclavian, 

 and runs forwards to the tongue. The dorsal artery supplies the whole head and 

 partly also the tongue. This dorsal vessel may, upon each side in young 

 specimens of Crocodilus Niloticus, be seen to be continued back to the aorta by 

 a solid cord, and it is therefore obviously identical with the dorsal artery of 

 amphibia and lacertilia. 



The arterial system of the bird resembles closely that of the crocodile. The 

 ventral vessel, however, is very smaU, and, taking origin from the base of the 

 subclavian, does not reach so far forward as the tongue. The dorsal vessel 

 supplies the tongue and the whole of the head, and is iisually called ' common 

 carotid artery.' It is sometimes to be found connected with the aorta by a solid 

 cord as in the other groups. 



As in aU the groups less advanced than mammals the branches to the external 

 aspects of the skull are dor.^^al in origin, it is probable that the external carotid 

 artery of mammals ought also to be regarded as developed from a dorsal trunk. 

 In all the different classes the branches of the dorsal carotid trunk are freely 

 connected bv longitudinal anastomosing chains with those of the dorsal aorta. 

 In the frog the occipital arten' is prolonged from the subclavian to anastomose 

 -with, branches of the dorsal carotid upon the skull. In the lacertilia an inferior 

 thyroid artery anastomoses with a branch of the carotid passing backwards. In 

 chelonia an occipital and a deep cervical artery form an anastomosis, while in 

 birds and crocodiles the vertebral artery marks an anastomotic chain. In the 

 mammal these three chains are all present as a rule, and two of them pass 

 between the external carotid and subclavian arteries. It is probable, therefore, 

 that the branches of the external carotid of the mammal are to be compared to 

 those of the dorsal carotid of other forms. The ventral carotid vessel in the 

 lower forms passing as far forwards as the tongue, but almost entirely continued 

 into the subclavian in crocodilia and aves, would seem to be represented in the 

 mammal by the thyroidea ima artery, a vessel rare in the human subject but 

 constant in the cetaceae. 



7. The Development of the Supra-renal Capsules in Man. 

 By Dr. C. S. Minot. 



3I0NDAY, SEPTEMBER 5. 

 The following Papers were read : — 



Bipcussion on ' Are Acquired Characters Hereditari/ ? ' in which Professor 

 Laxkester, Professor Weismann, Professor Hubrecht, Patrick Geddes, 

 M. Hartog, and E. B. Poulton took part. 



3 c 2 



