THE SKULL OF CIIIM.KRA. 12'.) 



mention of the cnitilnge e. He sliows, in one of liis figures, 

 a so-called Na.senfliigelknorpel, wliich is said to be longer than 

 the premaxillary cartilage, to lie directly mesial to it, and to be 

 derived from the nasal capsule. . This cartilage, as shown in 

 Vetter's figure, is not found in CJhimcera colliei, and it is not 

 shown in Hubrecht's figures of Chimcera moiistrosa. Its dorsal 

 end corresponds, in position, to the lateral rostral process of 

 these fishes, the remainder of it apparently being the cartilage m- 

 of Hubrecht's descriptions, or both that cartilage and the 

 cai-tilage hn. 



My conclusions regarding the homologies of these several carti- 

 lages differ somewhat from those of these several aiithois, and 

 tliey are based on my interjiretation of the lips and nasal aper- 

 tures of this fish as set forth in the work already several times 

 referred to as now in press (Allis, 1917 h), and which should here 

 be consulted. 



In the Pla.giostomi it is always that pait of the ala nasalis that 

 encircles the antero lateral and ingi^ess nasal aperture that is the 

 most developed, the part that encircles the ppstero-mesial and 

 egress aperture alwaj's being less developed and in some cases 

 wholly wanting. In Chimcera, on the contrary, it is the pa it of 

 this cartilage that encircles the antero-mesial and here so-called 

 ingress aperture that is the most deve!op)ed, that part of the 

 cartilage that encircles the antero-lateral and originally ingress 

 aperture having undergone marked reduction. That part of the 

 cartilage that encircles tlie antero-mesial aperture is lepresented 

 in the cartilage Icn of Hubrecht's descriptions, the cartilage k 

 representing that pai't of the ala nasalis of the Plagiostomi that 

 lies mesial to and between the processes h. and /3 of Gegenbaur's 

 (1872) descriptions of the latter fishes, and the process n of the 

 cartilage k representing the process a of the Plagiostomi together 

 with the process that Gegenbaur calls, in Mustelus, the process a . 

 The process /3 of the Plagiostomi is represented in Chimrera in 

 the little crescentic cartilage that lies in the ridge on the internal 

 surface of the naso-labial fold, and a, remnant of that part of 

 the ala nasalis that originally lay between this process and the 

 process a is represented in the cartilage I of Chimcera. 



The cartilages ')n and g of Chhvcrra have no homolognes in the 

 Plagiostomi, but they, the nasal-fold process of the cartilage g, 

 and the little adjacent crescentic cai'tilage are all evidently of 

 fibi-ous origin and all quite certainly ch on drifi cations of a sub- 

 epidermal layer of fibrous tissue. Just what this layer of tissue 

 is I have been unable as yet to definitely determine, but it would 

 seem to be the fibrous layer of the corinm. The nasal-flap carti- 

 lage of my descriptions of Rata (Allis, 1916) is certainly a 

 chondrification of this same layer of tissue, and as the process Jt 

 of the ala nasalis of that fish has exactly the same subepidermal 

 position as the nasal-flap cartilage, that process must also be of 

 fibrous origin. But, if this process a is of fibrous origin, the alar 

 ring, of which it is a process, must also be of similar origin, all 



