291 



Id the adult, Allen's drawings show the ophthalmica magna artery 

 arising from the efferent pseudobranchial artery (his internal or anterior 

 carotid) a perceptible distance before that artery falls into the internal 

 carotid (his communicating branch from external to internal carotid), 

 and this must, of course, have been the original disposition of the 

 vessels; a similar arrangement being shown in my figures of these 

 vessels in 12 mm and 50 mm larvae of Amia (Allis, 1900). In my 

 larvae of Polyodon the dorsal portion of the efiferent pseudobranchial 

 (mandibular) artery, the portion that lies between the ophthalmica 

 magna branch and the point where the artery falls into the internal 

 carotid (lateral dorsal aorta), has simply become so short as to have 

 practically disappeared. 



This finishes the description of the vessels that I have investigated, 

 excepting only the jugular vein, and this vessel was investigated only 

 in so far as its branches accompany, more or less closely, the carotid 

 arteries. The jugular vein, traced forward from the hind end of the 

 skull, enters the posterior opening of the facialis canal, there im- 

 mediately giving off a branch which accompanies the hyo-opercularis 

 artery. The vein then traverses the facialis canal with the external 

 carotid, issuing with that artery through the anterior opening of the 

 canal. The vein and artery then lie, in larvae, in a pronounced 

 groove on the lateral surface of the skull, this groove extending for- 

 ward from the anterior opening of the facialis canal to the trigeminus 

 foramen, and being found definitely marked in certain skulls of the 

 adult but not in others. Running forward in this groove, the vein 

 gives off three branches, one of which accompanies those branches 

 of the external carotid that go to the muscles of the region, a second 

 that perforates the cranial wall, and a third that accompanies the 

 maxillo-mandibularis branch of the external carotid. The branch that 

 perforates the cranial wall is the internal jugular. Its canal runs 

 forward and mesially and opens, internally, into the trigeminus canal, 

 or foramen, or into the cranial cavity immediately posterior to and 

 continuous with that foramen. As this internal jugular vein traverses 

 its canal, or just as it issues from it, it sends a branch to the 

 pituitary fossa, and then separates into two portions, a cerebral vein, 

 which has anterior and posterior branches, and an orbital or orbito- 

 nasal vein. The latter vein turns laterally and forward and traversing 

 the trigeminus foramen with the trigeminus, lateralis and abducens 

 nerves, issues in the orbit, where it separates into optic, orbito-nasal 

 and ophthalmic portions. After giving off the internal jugular and 

 maxillo-mandibular 'veins, above referred to, the remainder of the main 

 jugular vein continues forward and was not further traced. 



19* 



