10 Macteay Memorrat Vouume. 
exact point of origin and relationship to other vessels varies somewhat, still the 
artery in question agrees in taking its origin from the efferent artery of the hyoidean 
hemibranch. Here again modifications have been produced by suppression of anterior 
gills and consequent changes in the arrangement of blood vessels connected with 
these. 
In the case of the posterior carotid* the point of origin varies somewhat from 
that which obtains in such forms as Mustelus and Callorhynchus. The differences 
may be regarded as due to the fact that the efferent artery of the hyoidean 
hemibranch is not connected directly, as it is in the latter forms, with an epibranchial 
artery. In Callorhynchus, at all events it arises from such a connecting vessel, 
whilst in Ceratodus it does not, and we may probably regard the posterior carotid 
as equivalent to the latter artery proper together with the proximal portion of a 
suppressed epibranchial artery belonging formerly to the hyoidean arch. The 
correctness or otherwise of this can only be determined by a study of the develop- 
ment of the vessels. In its origin the posterior carotid of Ceratodus corresponds 
closely to the internal carotid of Rana, though, at the same time, the distribution of 
the latter is rather that of the vessel above described as anterior carotid. As Parker 
points out,t the use of the name “carotid” in regard to the vessels of fishes, &c., 
“must be taken to imply nothing more than a general correspondence with the 
similarly named vessels in the higher vertebrata.” 
(e) From the united first and second epibranchial arteries (figs. 2 and 5). 
Immediately behind the pomt of union of the first and second epibranchial 
arteries there arises a comparatively small vessel which runs directly upwards behind 
the skull and in front of the first modified rib. From its position it may be called 
the occipital artery (figs. 5 and 14, occ. art.). At about the level of the spinal 
cord it divides into two branches. The first of these continues the course of the main 
vessel and runs directly upwards to supply the muscles of the mid dorsal surface 
immediately behind the skull. The second turns backwards and gives off three 
branches, (a) one running to the side of the vertebral column—the anterior vertebral 
artery, (b) one running towards the surface through the muscles in the body wall 
behind the shoulder girdle ; in all probability this runs to the level of the lateral 
cutaneous vein, to be described later and accompanies this in its course and (c) one 
which runs downwards and round the anterior margin of the first rib—the costal 
artery. 
* Cf. Parker. loc. cit. p. 695, figs. 1 and 7, 
+ Loc. cit. p. 693. 
