88 ' ALUS. [Vol. XVIII. 



Inside the chamber there are four openings leading into canals 

 in the petrosal. Three of these canals are simply foramina that 

 lead through the side wall of the skull into the cranial cavity, and 

 serve, one for the exit of the truncus ciliaris, and the other two for 

 the exits of the anterior and posterior trunks of the trigemino- 

 facial ganglion. As the truncus ciliaris arises from the pro- 

 fundus ganglion, the foramen by which it issues from the cranial 

 cavity is the profundus foramen of the fish. It usually lies slightly 

 ventral, or ventro-anterior to the anterior one of the other two 

 foramina, which are respectively the trigeminal and facial foram- 

 ina. Whether these three openings leading from the cranial cav- 

 ity into the trigemino- facial chamber, or the two external openings 

 of the latter chamber, are the strict homologues of the correspond- 

 ing foramina described in other fishes seems open to some question. 

 The fourth opening in the chamber leads into a small, but rela- 

 tively long canal, which traverses the thin, ventral portion of the 

 body of the petrosal to its antero-ventral edge, and there opens 

 into the eye-muscle canal immediately at or slightly behind the 

 hind edge of the lateral wing of the parasphenoid. It transmits 

 the ramus palatinus facialis, and can accordingly be called the 

 palatine canal. It is, however, the approximate homologue of the 

 palatine foramen of Amia, and not at all the homologue of the 

 canal described by me as the palatine canal in that fish. 



The trigemino-facial chamber of Scomber was apparently not 

 recognized by Stannius, or possibly, though it seems hardly 

 probable, it did not exist in the specimens examined by him. 

 Whether, in the latter case, it had not been formed at all, or had 

 been formed and then separated into two parts by the later forma- 

 tion of a bony partition between the openings of the canals that 

 trasmit the facial and trigeminal nerves, is impossible to tell 

 from the descriptions ; for, while the communicating branch from 

 the truncus trigemini to the truncus facialis is said by Stannius 

 to lie outside the skull (No. 70, p. 47), the canal for the palatinus 

 facialis is said to be a branch of the canal that transmits the nervus 

 facialis, and to lie " zwischen den gesonderten Austrittstellen des 

 N. trigeminus und N. facialis" (No. 70, p. 55). The profundus 

 canal and foramen are not mentioned bv Stannius. 



