1876.] 



PROF. T. H. HUXLEY ON LEPIDOSIREN. 



181 



latter are the edges of the fold which overhang the mandible on each 

 side when the parts are undisturbed. They occupy the maxillary 

 region of the head, and may be termed the maxillary lips. 



The median portion of the anterior contour (a b) does not belong 

 to the lips at all, but corresponds, as is easily seen in a section of 

 the skull, with the anterior extremity of the chondrocranium and 

 the ventral edges of the nasal capsules. The line a b is, in fact, 

 the anterior contour of the head ; and the pigment-cells of the dorsal 

 integument are here continued onto the ventral face. After a very 

 short distance, however, the integument terminates in a slight, trans- 

 verse, papillose ridge, which forms the anterior boundary of a shallow 

 median depression ; on each side of the hinder part of this depression 

 is one of the vomerine teeth (v.t). 



Under view of the fore part of the roof of the mouth and underside of the head 

 of a young specimen of Lepidosiren anncctens ( X 3). a b, anterior 

 margin of the head; ac, b d, right and left maxillary lips: a.n, 

 anterior nasal apertures ; p.n, posterior nasal apertures ; u.l, praj- 

 maxillary lip ; v.t, vomerine teeth ; p.t, palatine teeth. 



The anterior nares (a.n) lie immediately behind the anterior 

 contour of the head ; and their more prominent posterior lips lie in 

 front of a transverse line drawn through the edge of the papillose 

 ridge. It is obvious that the area included between the anterior 

 contour of the head in front, the median fossa behind, and the 

 anterior nares at the sides, corresponds with the region occupied by 

 the naso-frontal process in the vertebrate embryo and with the homo- 

 logous large, shield -shaped, naso-frontal integumentary plate in the 

 Rays and Dogfishes. The papillose ridge (u.l) is therefore the 

 middle or premaxillary portion of the upper lip ; and if this be so, 

 it follows that the anterior nares in Lepidosiren are placed as in 

 Cbimseroids and Plagiostomi, on the under aspect of the head and 

 outside the mouth. 



I may add that Lepidosiren has two upper labial cartilages — one 

 fibro-cartilaginous immediately behind the anterior nasal aperture, 

 and the other behind the posterior nasal aperture. These answer 

 to the upper labial cartilages in Chimcera and Cestracion. 



