Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 93 



The orbital openings of the eye-muscle canal give passage, on 

 each side, to two of the recti muscles, the externus and internus, 

 to the internal carotid artery, to the ramus palatinus facialis, and 

 to a large venous vessel. The rectus superior arises at the edge 

 of the opening. The large venous vessel is formed by the union 

 of two veins that come from the nasal pit, through the olfactory 

 canal in the antorbital process, with a third vein that comes from 

 the eye-ball. The course of this vessel after it entered the eye- 

 muscle canal was not traced. As it is evidently, in part at least, 

 the homologue of the vein described by me in Amia as the vein vo 

 (No. 4) it probably communicates, in the eye-muscle canal, with 

 the corresponding vein of the opposite side of the head, and re- 

 ceives, or gives a branch to the hypophysis and saccus vasculosus. 

 The internal carotid artery, on each side, turns upward immedi- 

 ately in front of the basisphenoid and enters the cranial cavity, 

 receiving, as it turns upward, a delicate communicating branch 

 from the efferent artery of the opercular gill, which is the arteria 

 ophthalmica magna of the fish. This same communicating branch 

 is found in Amia (No. 4). 



The orbital opening of the eye-muscle canal of Scomber is thus 

 the morphological equivalent, in the structures it transmits, of 

 the ventral part, and that part only, of the orbital opening of the 

 canal in Amia. The internal carotid artery and the ramus pala- 

 tinus facialis which, in Scomber, enter the eye-muscle canal, and 

 issue from it by its orbital opening, form no exceptions to this 

 statement, for both these structures would, in Amia, of necessity 

 lie in, and issue from the orbital opening of, the eye-muscle canal, 

 if the hypophysial fenestra of Amia were to be enlarged, and the 

 cartilage of the basis cranii in front of it disappear, as it has in 

 Scomber. 



In Amia, the dorsal part of the orbital opening of the eye- 

 muscle canal, which lies anterior to the shank of the alisphenoid, 

 gives passage to the nervus trochlearis, radix profundi, nervus 

 oculomotorius, and an orbital extension of the jugular vein, the 

 two latter structures lying near the middle of the opening, ven- 

 tral to the other two. In Scomber, the trochlearis issues from 

 the cranial cavity along the anterior edge of the alisphenoid, 

 through the lateral edge of the large orbital opening of the brain 



