C)4 ALUS. [Vol. XVIII. 



case; the oculomotorius through a special foramen between the 

 lateral wing of the basisphenoid and the adjoining edges of the 

 alisphenoid and petrosal; and the truncus ciliaris profundi 

 through the anterior opening of the trigemino-facial chamber, 

 after having first perforated the cranial wall by a special foramen. 

 The trochlearis of Scomber thus has the same relations to the ali- 

 sphenoid that the trochlearis of Amia has. The oculomotorius of 

 Scomber, lying between the edges of the bones that separate the 

 orbital opening of the brain case from the orbital opening of the 

 eye-muscle canal, has simply been caught between those bones as 

 they, in their development, cut the single opening of Amia into the 

 two or more parts found in Scomber and certain other teleosts (No. 

 5). The truncus ciliaris profundi of Scomber has been similarly 

 caught in the region between the alisphenoid and petrosal, but has 

 been somewhat displaced from the position it has in Amia. In 

 embryos of Amia, where it alone was traced, the orbital extension 

 of the jugular vein is connected, just as it leaves the orbit, by a 

 short commissure with the vein described as the vein vo. Having 

 entered the upper lateral chamber of the eye-muscle canal it trav- 

 erses that chamber and issues posteriorly by the facial foramen. 

 In Scomber, where the anterior extension of the jugular vein 

 traverses the trigemino-facial chamber, no commissure connecting 

 it with the apparent homologue of the vein vo could be found in 

 the specimens examined, none of which however had been in- 

 jected. 



The trigemino-facial chamber of Scomber is thus seen to be 

 the homologue of the upper lateral chamber of the eye-muscle 

 canal of Amia in that it is traversed by the anterior extension of 

 the jugular vein, and that from it the facial, trigeminal and pro- 

 fundus nerves have their ultimate exits from the skull. In other 

 respects it differs greatly from the chamber of Amia, and, if any 

 homology exists, it can certainly be the exact homologue of a small 

 part only of that chamber. 



In Acanthias embryos Sewertzoff (No. 69) describes an ah- 

 sphenoid cartilage that is said to lie, in the earliest stage described 

 by him, between the nervi facialis and trigeminus behind, and the 

 nervi oculomotorius and opticus in front. The relation of the 

 cartilage to the nervus trochlearis is not given. At a later stage, 



