MUSTELUS L.EVIS. 105 



end of the cartilaginous nasal capsule, about midway between 

 it and the ectoderm, and the transverse sections that here cut 

 the region where the canal anastomoses with the infra-orbital 

 canal cut also the hind end of the nasal epithelium. The 

 canal at this point lies considerably lateral to the free, ventro- 

 lateral edge of the cartilage of the nasal capsule, but as it 

 runs forward from here it approaches this free edge of the 

 cartilage, and opposite the hind edge of the external nasal 

 aperture lies but slightly lateral to it. 



Opposite the nasal aperture the canal passes mesial to the 

 vei'tical plane of the free ventro-Iateral edge of the cartilage 

 of the capsule, and there lies in a depression on the lateral 

 portion of the internal, or dorsal, surface of what I take to be 

 the anterior process of Gegenbaur's (23, p. 99) descriptions 

 of the '' nasenfliigel" cartilage of the fish. In my specimen 

 this nasal-flap cartilage was wholly separate from and inde- 

 pendent of the cartilage of the nasal capsule. It, however, 

 closely approached anteriorly the ventral edge of the mesial 

 wall of the capsule, and posteriorly similarly approached the 

 ventral edge of a part of the lateral wall. The anterior pro- 

 cess of tiie cartilage is strongly curved in transverse section, 

 the back of the curve being presented dorso-laterally, and 

 the cartilage being so placed that its lateral edge, which is 

 directed ventro-laterally, lies ventral to, or even ventro- 

 lateral to the ventral edge of the lateral wall of the capsule. 

 Near this lateral edge of tiie nasal-flap cartilage there is, on 

 its dorsal sni'face, a slight longitudinal ridge. The portion 

 lateral to this ridge is slightly concave, is presented dorso- 

 laterally, and lodges the supra-orbital canal as it passes along 

 the region of the cartilage. The canal thus here has a 

 definite relation to the nasal-flap cartilage. 



Anterior to the nasal-flap cartilage the canal lies, for a 

 time, ventro-Iateral to the rounded, bulging, lateral surface 

 of the anterior end of the cartilage of the nasal capsule. 

 Continuing its course beyond the capsule it there has no rela- 

 tion to any underlying skeletal structure, until it reaches the 

 point where it turns upward on to the dorsal surface of the 



