256 MR. E. P, ALIilS ON THE OTIC EEQION OF 



cranium instead of the chondrocraiiium, excepting, possibly, in 

 fishes such as Moxostoma, where the latero-seiisory ossicles have 

 not, in this region, fused with the underlying bones. There is, 

 in all of these fishes in which there is an opisthotic bone, a more 

 or less developed opisthotic ridge, which runs antero-ventrally 

 from the summit of the suprascapular process of the opisthotic 

 towards the facialis opening of the trigemino-facialis chamber, 

 and it must, primarily, have ended, anteriorly, in the dorsal edge 

 of that opening. The vena jugularis, after it issues from the 

 facialis opening of the trigemino-facialis chamber, runs posteriorly 

 ventral to the opisthotic ridge, thus lying considerably ventral to 

 the spheno-pterotic ridge and in no relation whatever to it. 

 The subtemporal fossa., when present, lies dorsal to the opisthotic 

 I'idge, and the adductor and levator operculi, and the levatores 

 arcuum branchialium, have theii' origins either on, or dorsal to 

 the latter ridge, the surface of origin lying, in the Teleostei, 

 in part on the secondarily developed posterior process of the 

 pterotic. 



In the Selachii the conditions are somewhat difi"erent from 

 those above described, and this is unquestionably related to the 

 fact that the hyomandibula of these fishes has been developed 

 from the epihyal, instead of from the braiichial-rMy bars of the 

 hyal arch. Appaiently related to this, the lateral semicircular 

 canal lies lateral to the auditory vesicle (sacculus ?) and in a 

 nearly horizontal position. 



In Acanthias, both Gegenbaur (72) and Wells ('17) show, on 

 the dorsal surface of the chondrocranium, ridges which are said 

 to mark the positions of the anterior and posterior semicircular 

 canals. Between these two ridges, mesial ly, and the dorso-lateral 

 edge of the chondrocranium laterally, there is a slight depression 

 Avhich, according to Wells's figures, forms the surface of insertion 

 of a poi^tion of the trunk-muscles, but I find it giving insertion 

 to those muscles in its posterior portion onl}', its anterior 

 portion being occupied by a tough ligamentous structui'e which 

 has the appearence of being a tendinous anterior extension 

 of the trunk-muscles, but is not actually a tendon of those 

 muscles. This depression is thus a supraotic depression similar 

 to that in the Holostei and Teleostei, but it coixesponds to the 

 mesial portion, only, of the depression of the latter fishes, for 

 the dorso-lateral edge of this portion of the chondrocranium lies, 

 in Acanthias, considerably dorsal to the ridge of the lateral 

 semicircular canal, separated from it by a lai'ge concave surface 

 which lies on the lateral surface of the chondrocranium and gives 

 insertion to the levator maxillte superioris (CsdJ and the muscle 

 Csd,. The lateral edge of the supraotic depression forms, as above 

 stated, the dorso-lateral edge of the chondrocranium, it begins 

 anteriorly at the siunmit of the postoi-bital process, and the main 

 infraorbital latero-sensory canal lies superficial a.nd slightly mesial 

 to it. This edge of the depression, which is called by Wells the 

 , supraotic crest, is therefore certain!)^ the homologue of the spheno- 



