LABIAL CARTILAGES OF RAIA CLAVATA. 
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portion of the labial, in Raia, and the relations of the canal 
itself to the lateral portion of the labial are both against the 
view that these cartilages are developed in direct relation 
to the canal, but the cartilage of Raia is nevertheless 
evidently of fibro-cartilaginous origin, for sections of it 
show certain fibrous strings in the interior of the cartilage. 
They are, however, much less numerous than in the nasal- 
flap cartilage. 
Gegenbaur considered the anterior and posterior upper 
labials of his descriptions of the Selachii, and their assumed 
liomologues in the Batoidei, to be cartilages that served as 
groundwork (Grundwerk) on which the premaxillary and 
maxillary bones, respectively, of the Teleostei were developed. 
My work has as yet offered nothing decisive either in favour 
of or against this view, in so far as it applies to the two 
labials of the Selachii and the one upper labial of the present 
descriptions of Raia, but the relations of the labial of Raia to 
the branches of the nervi buccalis and trigeminus favour the 
view that its two portions may represent the two bones of the 
Teleostei. There is, however, doubt as to which part of the 
labial represents the maxillary and which the premaxillary. 
The nasal-flap cartilage, Gegenbaur’s anterior labial, can not,, 
however, represent either of the two bones of the Teleostei. 
Its general position, in Raia, and its relations, in Myliobatis,. 
to the so-called Trager der Nasenfliigelknorpel, strongly 
suggest that it may represent the ascending process of the 
premaxillary bone of the Teleostei, and that the Trager der 
Nasenfliigelknorpel may represent the rostral cartilage of 
certain of those fishes. 
In two of my earlier works (1898, 1909) I came to the 
conclusion that the ascending process of the premaxillary 
bone of the Teleostei was primarily an independent bone,, 
the so-called dermal ethmoid, which later fused with the 
premaxillary. This primarily independent bone was said to 
have been developed in protective relation to a line of latero- 
sensory organs, and to be found as such a protective bone 
not only in certain ganoids (Amia, Polypterus), but also in 
