587 



branchial canal and the horizontal portion of the corresponding carotid 

 canal, there is a very slight depression on the dorsal surface of the 

 cartilage of the basis cranii. This depression lodges the canalis 

 transversus, but whether that canal lies between the cartilage and 

 its lining membrane, or wholly enveloped in the membrane, could 

 not be determined in my specimens. This canal opens on the side 

 wall of the skull by a foramen that lies between the trigeminus and 

 efferent pseudobranchial foramina, and it transmits a vessel that is 

 apparently venous and that must be the pituitary vein, but its origin 

 and connections could not be determined. The canalis transversus, or 

 pituitary canal of this fish, and the carotid and pseudobranchial canals 

 all accordingly lie morphologically in the basis cranii, and they all 

 are strictly comparable with the canals in Heptanchus. 



Gegenbaur (1872), in his figures of Eaja, does not show either 

 the carotid or pituitary canals, nor does he show their foramina. 

 He however shows a foramen in the side wall of the skull that is not 

 index-lettered but which has the position of the efferent pseudo- 

 branchial foramen in my specimen. Of the carotid canal he says 

 (1. c. p. 75): "Bei den Eochen vereinigen sich die beiderseitigen Caro- 

 tiden an der Basis cranii; von wo sie dann ein engerer Canal in die 

 Schädelhöhle führt." And in Ehynchobatus he shows such a single, 

 median, carotid canal. Of the canahs transversus he says (1. c. p. 76) : 

 "Bei Eaja beginnt er vor und unterhalb der Trigeminusöffnung und 

 leitet in einen ganz von der Dura mater umwandeten, die Innenfläche 

 der Schädelbasis quer durchziehenden Canal." 



The external carotid, after its separation from the internal 

 carotid, runs forward ventral to the nervus opticus, and at the anterior 

 edge of the orbit separates into two parts one of which goes to the 

 fronto-nasal region and the other to the mandible. Close to its point 

 of origin it gives off a branch which runs forward dorsal to the nervus 

 opticus and, accompanying the opthalmicus nerves, reaches the dorsal 

 surface of the snout. At the base of the external carotid, in the angle 

 between it and the lateral dorsal aorta, a small branch arises which is 

 undoubtedly the arteria bronchialis of Hyrtl's descriptions of Eaja 

 clavata, said by that author to go to the anterior wall of the spiracle. 

 In my specimens of Eaja radiata it sometimes had that distribution, 

 but in the one specimen used for illustration it joined and fused with 

 the efferent pseudobranchial artery, thus suggesting an artery sim- 

 ilar to the secondary afferent pseudobranchial artery in Salmo and 

 Gadus (Allis, 1912a). 



