Prof. Reid on the Voo-marus Islandicus. 467 



'O 



the appearances just described, as observed by the aid of a com- 

 mon pocket lens. 



The posterior, lateral and superior walls of the cavity of the 

 cranium appear to the unaided eye to be composed of fibro- 

 cartilage, exhibiting no traces of a division into separate por- 

 tions ; and a deep groove extending between the superior mar- 

 gins of the orbits, runs along th^ whole of the superior surface 

 of the cranium, in which the elongated nasal processes of the 

 intermaxillary bones are contained. The floor of the anterior 

 part of this groove is occupied by the cartilaginous anterior frontal 

 bones, which are raised into a well-marked ridge in the course of 

 the mesial line of the cranium. The two intermaxillary bones are 

 united at the mesial line and are prolonged outwards and down- 

 wards along the margin of the mouth to the commissure of the 

 lips. The two nasal processes of the intermaxillaries — one from 

 each intermaxillary — extend backwards over the middle portion 

 of the maxillary bones, along the groove on the superior surface 

 of the cranium as far back as the crest of the superior occipital, 

 becoming narrower as they proceed backwards. The posterior and 

 middle portions of both these processes lie in and are firmly fixed 

 in a single groove on the superior surface of a portion of cartilage 

 exceeding them in depth as well as in thickness, which also sends 

 downwards a very thin ridge along the centre of a deep and wide 

 groove in the anterior portion of these processes. This portion of 

 cartilage is also grooved along its inferior surface and in the same 

 line with that in the nasal processes of the intermaxillaries, but 

 the former is considerably less deep and wide than the latter. 

 These two grooves can be made to move freely upwards and 

 downwards over the ridges on the upper surfaces of the maxillary 

 and anterior frontal bones, and the snout can be thus protruded 

 or retracted. The difference between the structure of the fibrous 

 nasal processes of the intermaxillary, and that of the portion of 

 cartilage firmly embracing their posterior and middle portions, 

 was very well marked*. The superior maxillary bone consists 

 of two distinct parts. First, a central part placed in front of the 

 vomer and anterior frontals and behind the body of the inter- 

 maxillary, loosely connected to the former by fibrous tissue, and 

 more closely, but not sufficiently so to prevent motion between 

 them, to the latter. It was in close apposition, but not immove- 

 ably connected to its fellow of the opposite side, was about an inch 

 and a half in length, and considerably broader at its anterior than 

 at its posterior half, which was very narrow. The broadest part, 

 which was a little behind the anterior extremity, was half an inch 

 in breadth, and from its outer edge a broad thin plate of fibrous 



* Is this mass of cartilage the homologue of the nasal bones? 



30* 



