586 



by the fusion of the efferent hyoidean and glossopharyngeus arteries, 

 or it must represent one or the other of those two arteries, the other 

 then being wanting. Neither of these suppositions being probable, 

 and neither of them agreeing with the conditions shown in Parker's 

 lateral view of these same arteries, it is evident that there is some 

 error here. 



The common carotid artery, in Eaja radiata, runs dorso-antero- 

 mesially and having passed the anterior edge of the hyomandibular 

 and reached a point dorso-mesial to the pseudobranch separates 

 into its external and internal branches. 



The internal carotid, which is the anterior prolongation of the 

 lateral dorsal aorta, turns mesially, and, lying immediately ventral 

 to the base of the chondrocranium, meets and anastomoses with 

 its fellow of the opposite side, in the median line, to form a single 

 median artery. This median artery turns upward and imme- 

 diately enters the carotid canal in the cartilage of the basis cranii, 

 this canal beginning by a single median opening instead of by two 

 openings, as in Heptanchus (Allis, 1912b). Eunning upward, the 

 artery and canal each soon separates into two parts, one on either 

 side, as in Heptanchus, and each of these branch canals, each enclosing 

 the corresponding artery, opens independently on the dorsal surface 

 of the cartilage of the basis cranii, between that cartilage and the 

 thick hning membrane of the cranial cavity. There each artery turns 

 laterally and slightly forward, lying between the cartilage and its 

 lining membrane and thus, morphologically, still in a canal in the 

 basis cranii. The artery then soon turns upward and forward, nearly 

 at a right angle, pierces the overlying lining membrane and definitely 

 enters the cranial cavity proper. There it runs directly forward, sends 

 an optic branch outward to the eye-ball, with the nervus opticus, and 

 then separates into two parts one of which is the anterior and the other 

 the posterior cerebralis artery. At the angle where the carotid canal 

 turns sharply upward and forward to pierce the overlying membrane 

 and definitely enter the cranial cavity, it receives a canal that transmits 

 the efferent pseudobranchial artery, that canal first perforating the 

 side wall of the skull and then, hke that portion of the carotid canal 

 into which it empties, lying on the dorsal surface of the cartilage of the 

 bais cranii, between that cartilage and its Uning membrane. 



Immediately posterior to the continuous and transversely placed 

 canal formed, on either side of the head, by the efferent pseudo- 



