BLOOD-VESSELS OF MUSTELUS ANTARCTICUS. 
695 
supposing the embryonic blood-current to undergo the reversal which is pre-supposed 
by Hyrtl’s view of the circulation through the pseudobranch. 
(2.) The posterior carotid artery. 
Carotis posterior y. Carotis interna posterior, Muller (17). 
Carotisposterior, Stannius (25). 
Carotide interne posterieure, Milne Edwards (14). 
Carotis communis plus Carotis externa, Hyrtl (11). 
The course of the posterior carotid has already been partly described (p. 690). From 
its origin from the first efferent branchial artery it passes forwards and inwards 
(Plate 35, fig. 6, Post. car. A.) along the ventral face of the hyomanclibular and 
auditory capsule, and enters the orbit through a foramen in its cartilaginous floor. 
The anastomotic trunk w, already referred to (Carotis interna, Hyrtl), is given off just 
before entering this foramen; it passes inwards and slightly forwards along a groove 
on the skull floor. The groove soon becomes a canal through which the vessel in ques¬ 
tion reaches the pituitary space, where, imbedded in the thickened perichondrium, it 
crosses its fellow of the opposite side and unites with the anterior carotid of the 
opposite side, as already described (p. 694). The anastomotic trunk from the left 
posterior carotid passes ventrad of that from the right: Hyrtl found exactly the 
opposite arrangement in Raja clavata. 
In Hyrtl’s paper (11) the posterior carotid, from its origin to the point of junction 
of the trunk w, is called the “ common ” carotid : the remainder of the artery is the 
“external” carotid, and the anastomotic branch w, the “internal ” carotid. I have 
adopted these names in my “ Zootomy ” (23), but have now come to the conclusion, 
as stated above (p. 693), that it is advisable to discontinue their use. That they were 
ever employed is a striking instance of the danger of basing a nomenclature on the 
study of specialized forms. 
Immediately after entering the orbit the posterior carotid gives off the orbital artery 
(Plate 35, figs. 6, 10, and 11, Orbit. A.). This sends off twigs to the posterior wall of 
the orbit, and then divides into two branches, a dorsal which supplies the superior 
rectus, superior oblique and inferior oblique muscles, and a ventral which supplies the 
internal and external recti. The inferior rectus apparently receives its blood supply 
from a special branch of the posterior carotid. 
The posterior carotid then passes obliquely forwards and outwards, emerging from 
the orbit at its antero-ventral corner (fig. 10); it then gives oft’ a large buccal artery 
to the M. adductor mandibulse, and almost immediately divides into two trunks, the 
maxillo-nasal artery which passes forwards and downwards along the anterior edge of 
the upper jaw (pterygo-quadrate cartilage), and a rostral artery (Rost. A.) which goes 
at first forwards, upwards, and inwards, then forwards and inwards along the outer 
border of the lateral (paired) rostral cartilage. 
