THE SKULL OF CniM-EIlA. 181 



distinct cartilages, capable of a slight motion with each otlier, 

 but they are later said to be so completely fused that there is 

 even but slight persisting indication of the line of separation 

 between them. Vetter found them as separate cartilages ami 

 considered them to be, respectively, the maxillary and mandibular 

 labials. K. Fiirbringer found them more independent of each 

 other tha.n they are said to be by Hubrecht, but less so than 

 described and figured by Vetter, and he agrees with Hubrecht 

 in considering them, together, to represent the posterior upper 

 labial. Luther shows them as a single cartilage, and they to- 

 gether form the maxillaiy, and hence posterior upper labial of 

 his descriptions. I find them as separate and distinct cartilages 

 lying immedia.tely posterior to the angle of the supplementary 

 secondary gape of the mouth and straddling the line prolonged 

 of that angle, that angle lying near the inner end of the line of 

 the angle of the gape, as fully described in my work now in 

 press ( Allis, 1917 b). One of these cartilages thus lies dorsal and 

 the other ventral to the line of the angle of the gape, in the 

 positions respectively of the posterior upper and mandibidar 

 labials of the Selachii, and I accordingly consider them, as 

 Vetter did, to represent, respectively, those labials, notwith- 

 standing that they both, and particularly the posterior upper 

 labial, seem to be chondrifications of the same fibrous layer that 

 has given origin to the cartilages g, m, and e of Hubrecht's 

 descriptions. 



The posterior upper labial, thus identified, is a small and some- 

 what rectangular cartilage that lies immediately dorsal (morpho- 

 logically posterior) to the ventro-posterior-lateral end of the 

 plate- like portion of the cartilage /gr. It is strongly but loosely 

 attached, by its ventral (morphologically anterior) end, to the 

 latter cartilage, and also strongly but quite rigidly attached, by 

 the adjoining, posterior (morphologically ventral) edge, to the 

 dorsal end of the mandibidar labial. This latter attachment 

 allows of but little motion between the two pieces, such little 

 motion as there is being latero-mesial. The labial gives inser- 

 tion, on its dorsal (morphologically posterior) edge, to the 

 musculus levator anguli oris anterior, and either on its external 

 surface or its anterior (moi-phologically dorsal) edge, to the 

 musculus labialis anterior, the other end of the latter muscle 

 being inserted on the dorso-anterior end of the cartilage /gr. 



The mandibular labial (cartilage c) is a stout bar of cai^tilage 

 with a large triangidar process on its anterior edge near its ventral 

 end. The anterior edge of its dorsal end is strongly attached to 

 the posterior upper labial, as just above described. Its ventral 

 end lies in the hind end of the labial part of the naso-labial fold. 

 Its anterior process passes internal to the hind end of the supra- 

 mandibular furrow, and lies in supporting relations to the sup- 

 plementary secondary lower lip, this process and the nasal-flap 

 process of the cartilage g, together with the related crescentic 

 cartilage above described, thus being opposed to each other in 



