MUSTELUS L.EVIS. 137 



through the ventral opening of the capsule, the branch then 

 turning mesiall}^ along the ventral surface of the skull, and, 

 at the middle line of the head, anastomosing with its fellow 

 of the opposite side. This large branch of the peri-orbital 

 sinus is thus certainl}^ the anterior facial vein of Parker's 

 descriptions of the adult. As it traverses its canal in my 

 embryos it is not accompanied by any other structure, so far 

 as I could find, certainly not by any branch of the ramus 

 ophthalmicus profundus. The canal is thus not the exact 

 equivalent of the orbito- nasal canal of Gegenbaui-'s descrip- 

 tions. But if it should, in the adult, become fused with the 

 profundus canal, to be later described, and that canal should 

 become wholly shut off, by cartilage, from the cranial cavity, 

 a canal would arise which would seem to be the equivalent 

 of Gegeubaur's canal. The canal, in my embryo, is quite 

 certainly the homologue of the orbito-nasal canal of my 

 descriptions of Amia (3, p. 514), and that canal is thus 

 probably not the exact homologue of the orbito-nasal canal 

 of Gegenbaur's descriptions of selachians. The name orbito- 

 nasal is, however, properly applicable to it. It is evidently, 

 in origin, wholly separate from and independent of the pro- 

 fundus canal. 



Another branch of the peri-orbital sinus of my embryos 

 traverses the canalis transversus, in exactly the manner that 

 Gegenbaur says that a branch of his lymph sinus traverses 

 the same canal in the adult (23, p. 77). This branch is not 

 described by Parker in his descriptions of the blood-vessels 

 of Mu steins an tare tic us. If, nevertheless, it be venous in 

 the adult Mustelus Itevis, as it certainly is in embryos, or 

 even if it is simply derived from a sinus that is venous in 

 embryos of the age of my oldest ones, the canal it traverses 

 must be quite differently judged, in any comparison with 

 teleosts, from what it Avould be if the vessel were a lymph 

 one of independent origin. The homology proposed by 

 Gegenbaur and Sagemehl (56) of this canalis transversus of 

 selachians with the eye-muscle canal of teleosts and ganoids 

 is, in fact, wholly based on the supposition that the canal in 



