442 . C. H. DANFORTH 



Although the foregoing account shows quite clearly that the 

 extensive system of vessels here described as the external caro- 

 tid (fig. 16) and its branches is really much more than is usually 

 embraced by that term, this designation is employed for conven- 

 ience in the description of a natural system, the parts of which 

 cannot be satisfactorily homologized by macroscopic methods 

 alone. The several interesting questions that naturally arise 

 in this connection must undoubtedly await embryological studies 

 for their final solution. 



INTERNAL CAROTID AND EFFERENT PSEUDOBRANCHIAL 



ARTERIES 



The internal carotid artery (fig. 15, a.ci.) is intimately con- 

 nected with the efferent pseudobranchial (a. eps.). It at first 

 runs anteriorly in the roof of the mouth, lying on the ventral 

 surface of the parasphenoid bone. Anteriorly it turns laterally 

 and, dorsal to an expansion of the bone, enters a canal in the 

 basis cranii, where it is soon joined by the efferent pseudobranch- 

 chial (a. eps.) which is the larger of the two. This vessel arises 

 in the pseudobranch from about twenty filamentar arteries and, 

 gaining the ventral surface of the protractor hyomandibularis, 

 passes forward across that muscle to a canal which it enters 

 at a point dorsal and anterior to the opening of the internal 

 carotid canal. The canals unite in front and the arteries within 

 anastomose. This anastomosis may apparently be effected 

 through a large connecting branch or more commonly the two 

 arteries completely fuse for a short distance. Anterior to the anas- 

 tomosis the internal carotid becomes the larger vessel and the 

 efferent pseudobranchial, now greatly reduced, proceeds as the 

 a. ophthalmica magna (fig. 15, a.om.). This artery, while still 

 in the cartilage, gives rise to several small twigs which could not 

 be traced far, and then escapes from the cranial wall above the 

 trigeminal nerve. It is at first posterior to the rectus muscles 

 and then comes to lie in between them, following an independent 

 course to the back of the eyeball which it enters just posterior 

 to the entrance of the optic nerve. X few small twigs may be 



