Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 87 



teriorly it is connected with a tendinous membrane which seems 

 to represent, as will be later shown, the first and second divisions 

 of the levator maxillae superioris muscle of the fish. 



The anterior opening of the chamber thus lies ventro-posterior 

 to the alisphenoid. It transmits, among- other structures, the 

 rami ophthalmicus superficialis and buccalis facialis, the ramus 

 ophthalmicus superficialis trigemini, the truncus maxillaris tri- 

 gemini, and the truncus ciliaris profundi. It is accordingly, in 

 a measure, the fused external opening of the foramina of those 

 several structures. In Amia the radix profundi, from which the 

 ciliary nerves arise, is transmitted through an opening that lies an- 

 terior to the alisphenoid, the ophthalmic and maxillary branches 

 of the trigeminus and the ophthalmic and buccal branches of the 

 facialis issuing by foramina that lie posterior to that bone. The 

 position of the single opening which, in Scomber, transmits all 

 these nerves, indicates that they have become so associated by 

 mutually approaching each other along the ventral edge of the 

 alisphenoid, in the sutural line between that bone and the basi- 

 sphenoid and petrosal, and not by traversing the alisphenoid. 

 There is, accordingly, nothing here to indicate that a nerve found 

 in front of a certain element of the skull in one animal can traverse 

 that element in another animal, and attain, in that manner, a posi- 

 tion behind it. The arrangement in Scomber seems, on the con- 

 trary, to show that when a nerve changes its position relative to a 

 bone it does so by passing around it instead of through it. 



The posterior opening of the chamber is flat, looks backward 

 and slightly upward, and lies approximately in the mid-vertical 

 line of the outer surface of the petrosal, slightly dorsal to its 

 middle point. A slight ridge runs backward, on the outer surface 

 of the bone, from each edge of the opening, the ventral ridge being 

 much more pronounced than the dorsal one. The slight groove 

 that lies between the two ridges marks the course of certain of the 

 structures that are transmitted by the opening. 



The chamber gives passage to a sympathetic nerve, to a com- 

 municating branch from the truncus maxillaris trigemini to the 

 truncus facialis, to the orbital branch of the jugular vein, and 

 to the external carotid artery. On the sympathetic nerve a large 

 ganglion is formed, which lies partly in the chamber and in part 

 immediately beyond its anterior opening. 



