130 



MR. E. PHELPS ALL1S, JUN., OX 



of these cartilages then being chondrifications of a single layer 

 of subepidermal fibrous tissue. This fibrous layer certainly 

 passed, originally, beneath the epidermal tissues that were modi- 

 fied to form the sensory epithelium of the nasal pit, and when 

 this sensory tissue was invaginated to form that pit, the fibrous 

 layer must have been invaginated with it. The nasal capsule 

 might then itself also be a chondrification of this same layer of 

 fibrous tissue, and hence not a part of the axial skeleton, as it is 

 usually considered to be ; and its development in the Plagiostomi 

 is decidedly in favour of this assumption. 



The cartilage f of Hubrecht's descriptions of Chimera, although 

 it lies along the edge of the postero-lateral nasal aperture, has no 

 relations whatever to the original antero-lateral nasal aperture, 

 and hence is not a derivative of the ala nasalis, and its position 

 strongly indicates that it is an anterior upper labial. It has 

 approximately the position of that labial in Heterodontus, and 

 also that of the single labial of Ceratodas (Allis, 1917 6), and 

 the fact that its anterior end is in contact with a part of the 

 chondrocranium that is quite unquestionably derived from the 

 palato-quadrate is in accord with the conditions that I have 

 above described in several of the Selachii, and would be wholly 

 exceptional for a cartilage derived from the ala nasalis. If, in 

 one of the Selachii above referred to, the fibrous or ligamentous 

 tissues that are related to the anterior upper labial, and that are 

 attached to the chondrocranium in the nasal region, were to 

 undergo chondrification, a cartilage would arise that would 

 closely resemble the cartilage fg of Chimcera, one part of this 

 cartilage thus being of labial origin and the other of independent 

 fibrous origin. Furthermore, this origin of the cartilage is in 

 accord with its relations to the terminal branches of the nervus 

 maxillaris trigemini, for the more important terminal branches 

 of that nerve pass internal to the cartilage, between it and the 

 nasal capsule, which is not their relations either to any part of 

 the nasal capsule of the Selachii or to the ala nasalis of those 

 fishes, but is their relations to the anterior upper labial and its 

 related ligaments in those fishes. What is apparently the carti- 

 lage fin Sehauinsland's descriptions of embryos of Callorhynchus 

 (1903, n 2 , fig. 127) has, however, decidedly the appearance of 

 being a part of the ala nasalis, but the cartilages as there shown 

 are so different from those in the adult Chimcera that I am 

 unable to make any comparison. Two of the cartilages de- 

 scribed by Scharuinsland, called by him the cartilages V and I 2 , 

 are said by him to lie in mucous folds " welche die Schnauze 

 umgeben " and to represent preoral visceral arches. Premancli- 

 bular arches they may represent, as may also the labial carti- 

 lages of the Selachii, but they certainly cannot represent preoral 

 arches. 



The cartilages c and d of Hubrecht's descriptions were con- 

 sidered by him to together represent the posterior upper labial 

 of the Selachii. They are first said by him to be separate and 



