THE SKI LL OK CUIM.LRA. 



123 



2. Nasal and Labial Cartilages. 



The so-called nasal and labial cartilages of current descriptions 

 of the Holocephali are much more numerous than the similarly 

 named cartilages of the Selachii, and the conditions in the latter 

 tishes must lirst be considered. 



The nasal cartilages of the Selachii are limited to the ala nasal is 

 (Nasenniigelknorpel), and this cartilage J have recently described 

 in a certain number of these tishes and compared it with the 

 cartilage in Chimwrci (Allis, 1917 b). It is accordingly not 

 necessary to here consider it in the former fishes. 



The labial cartilages of the Selachii are limited to one or two 

 related to the upper jaw and one related to the lower jaw. 

 Gegenbaur (1872) called the one or two former cartilages the 

 anterior and posterior upper labials, and as he at that time 

 considered the premaxillary and maxillary bones, respectively, of 

 the Teleostei to be developed superficial to, and in relation to, 

 these cartilages, he also called them the premaxillary and 

 maxillary labials. These latter *terms I shall avoid because 

 of the implied homologies, which I consider not yet established. 

 The single labial related to tire lower jaw Gegenbaur called the 

 lower, or premandibular labial, the latter term being used by him 

 because he then considered this labial and the maxillary labial 

 to together represent persisting remnants of a premandibular 

 visceral arch. This latter term I shall also avoid, using in its 

 place the indifferent term mandibular labial. If it should be 

 later established that this labial and one or both of the upper 

 labials are structures related to a premandibular arch or arches, 

 they can then be given names that will show their relations to 

 the arch or arches to which they belong. 



The hind end of the mandibular labial and the corresponding 

 end of one or both of the upper labials articulate with each other, 

 or are connected by ligament, immediately posterior to the outer 

 end of the line of the angle of the gape, and these ends of the 

 labials there lie at a certain distance from the cartilages of 

 the upper and lower jaws, separated from them by the thickness 

 of the anterior edge of the musculus adductor mandibular. This 

 point of articulation of the labials lies at a variable distance 

 anterior to the quadra to-mandibnlar articulation, and it is shown 

 in nearly all of Gegenbaur's figures of these fishes lying external 

 to the mandibula. 



In Chlamydoselachus there are two upper and one lower labials, 

 and they have been described or figured by Goodey (1910), K. Fiir- 

 bringer (1903), and Luther (1909 a). The anterior labial gives 

 attachment, along the dorsal edge of its anterior end, to a 

 ligament which has its origin on the anterior wall of the orbit 

 at about the middle of its height. Numerous short ligamentous 

 strings run from the a ntero- ventral edge of this ligament into 

 the tissues of the upper lip, this seeming to indicate that the 

 ligament has been differentiated from an extensive dermal or 



9* 



