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PROCEEDINGS OF THE CANADIAN INSTITUTE. 



and basioccipital, also enter into the protection of the auditory 

 apparatus, and that in Salmo (the only instance apparently observed 

 by him ) the epiotic does not contain the exterior semicircular canal. 

 The cartilage in which the occipital bones develop did not originally 

 form part of the auditory case, the passage of the semicircular canal 

 through the exoccipital and supraoccipital being secondary, as the 

 hollowing out of the basioccipital for the sacculus certainly is, so 

 that the names applied to these parts more truly indicate their origin. 

 Parker's paper on the skull of the salmon, 1 published later in the 

 same year, states that, contrary to Vrolik's opinion, the epiotic does 

 arise in connection with a semicircular canal, and shows also that a 

 similar relation occurs in the pterotic, sphenotic, and opisthotic. 



In the Selachii the auditory capsule is at first quite distinct from 

 the rest of the skull, with which it eventually fuses, and throughout 

 life remains without connection with the cranial cavity except by the 

 foramen for the auditory nerve. It lies at the sides of the skull, 

 but does not extend back to the occipital region. In young Teleosts 

 the cartilaginous capsule does not extend back as far as the occipital 

 region, lying still at the sides. Now all bones formed in this car- 

 tilaginous capsule are certainly entitled to be referred to the " otica " 

 group. The anterior portion of this capsule is ossified as the probtic 

 (petrosum), a tract of osteoblasts outside the ampulla of the anterior 

 semicircular canal gives origin to the sphenotic (postfrontal), the 

 pterotic (squamosal) arises over the ampulla and arch of the external 

 canal, the epiotic (occipital externum) over the arch of the posterior 

 canal, and the opisthotic (intercalare) over the ampulla of the same 

 canal. All these bones lie in the region occupied by the cartilagin- 

 ous auditory capsule, all are mainly what may be called cartilage 

 bones, 2 and all hold a more or less definite relation to the included 

 auditory apparatus. 



The terms prootic, sphenotic, pterotic, epiotic and opisthotic, applied 

 respectively to the bones known to German authors as the petrosum, 

 postfrontal, squamosal, occipitale externum, and intercalare, are pre- 

 ferable, as indicating the true relations of these ossifications. 



Sagemehl in his paper on Amia 3 makes many ingenious and 



1 W. K. Parke.)'. — The structure and development of the skull in the Salmon. Phil. Trans., 

 1873. 



* Gegenbaur's objections to the pterotic (Ub. das Kopfskelet von Alepocephalus rostratus 

 (Risso). Morph. Jahrb, Bd. IV., suppl., 1878,) have been shown above to be groundless. 



8 Ante cit. 



