THE SKULL OF CHIMJERA. 



129 



mention of the cartilage e. He shows, in one of his figures, 

 a so-called Nasenfiugelknorpel, which is said to he longer than 

 the premaxillary cartilage, to He directly mesial to it, and to he 

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

 Vetter's figure, is not found in Chimcera collie /, and it is not 

 shown in Huhrecht's figures of Chimcera mortstrom. Its dorsal 

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

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

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

 cartilage kn. 



My conclusions regarding the homologies of these several- carti- 

 lages differ somewhat from those of these several authors, and 

 they are based on my interpretation 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 b), and which should here 

 be consulted. 



In the Plagiostomi it is always that part of the ala nasalis that 

 encircles the antero lateral and ingress nasal aperture that is the 

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

 egress aperture always being less developed and in some cases 

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

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

 ingress aperture that is the most developed, that part of the 

 cartilage that encircles the anterolateral and originally ingress 

 aperture having undergone marked reduction. That part of the 

 cartilage that encircles the antero-mesial aperture is represented 

 in the cartilage kn of Huhrecht's descriptions, the cartilage k 

 representing that part of the ala nasalis of the Plagiostomi that 

 lies mesial to and between the processes oc and (3 of Gegenbaur's 

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

 cartilage k representing the process « of the Plagiostomi together 

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

 The process /3 of the Plagiostomi is represented in Chimcera 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 ci is represented in the cartilage I of Chimcera. 



The cartilages m and g of Chimcera have no homologues in the 

 Plagiostomi, but they, the nasal-fold process of the cartilage (/, 

 and the little adjacent crescentic cartilage are all evidently of 

 fibrous origin and all quite certainly eh on drifi cations of a sub- 

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

 is I have been unable as } 7 et to definitely determine, but it would 

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

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

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

 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 



