THE SKULL OF CHIMERA. 



125 



tissues to the mandibular labial, and can thus be said ,to articulate 

 with it. From near its hind end a ligamentous strand runs 

 antero-dorsally and joins a stouter ligament which arises from 

 the median transverse aponeurosis of the musculus adductor 

 mandibular, at the inner end of the line of the angle of the gape. 

 The ligament so formed is joined by a ligamentous slip from 

 about the middle of the anterior labial, and then joins and fuses 

 in part with the internal surface of the dorsal, maxillary portion 

 of the adductor muscle and in part with the closely related 

 musculus levator labii superioris. A part of the ligament 

 continues forward and is inserted on the posterior surface of 

 the nasal capsule at the lateral edge of the large surface of 

 insertion, on that capsule, of a part of the musculus levator 

 labii superioris. There are thus, in this fish, two ligamentous 

 structures connecting the upper labials with the nasal capsule. 

 In Chlamydoselachus this connection is, as just above stated, 

 with the antorbital wall. 



In Triakis fasciatum there are two upper labials, and they 

 closely resemble, in relative size and arrangement, those in 

 Mustelus. The hind ends of the two labials lie close together, 

 and both are bound by ligamentous tissues to the hind end 

 of the mandibular labial, but the posterior upper labial alone 

 articulates with that labial. The anterior end of the anterior 

 upper labial rests directly upon the external surface of the 

 palatoquadrate, as in Mustelus, but it is not enclosed in a 

 pocket of the connective tissues of the region. A broad stout 

 ligamentous band arises from the external surface of the palato- 

 quadrate, at its oral edge and slightly anterior to the angle 

 of the gape, and running antero-mesially across the external 

 surface of the anterior upper labial is inserted on the internal 

 surface of the nasal latero-sensory canal, close to the postero- 

 mesial edge of the nasal capsule. 



In two small specimens of Scyllium canicula I find, as 

 Gegenbaur did, but one labial, and it quite certainly corre- 

 sponds to the anterior upper labial of Mustelus, as Gegenbaur 

 concluded. It extends forward along the ventral edge of, or 

 slightly internal to, the musculus levator labii superioris, and 

 its anterior end lies, as does that of the anterior upper labial 

 of Mustelus, directly upon the external surface of the palato- 

 quadrate, in a slight depression in that cartilage, but it is not 

 enclosed in a pocket of connective tissue. This end of the labial 

 lies directly internal to the posterior portions of the nasal and 

 rostral sections of the latero sensory canals. In one of the two 

 specimens, but not in the other, the mandibular labial hooked 

 around the angle of the gape, as Luther (1909 a) shows it in 

 his figure of Chiloscyllium, this suggesting the possible fusion 

 of a much reduced posterior upper labial with the mandibular 

 labial. 



The anterior end of the anterior upper labial is thus, in each 

 of these few Selachii, either in contact with or closely related to 



