468 Prof. Reid on the Voffmarus Islandicus 



&' 



texture was prolonged outwards and downwards towards the 

 commissure of the lips, running posterior and parallel to the 

 body of the intermaxillary. The inferior surface of the thin 

 fibrous and superficial plate, with ridges on its external surface 

 similar to the opercular bones, covering the sides of the cheeks, 

 becomes inseparably blended with the superior sui'face of the 

 lateral fibrous prolongation of the central portion of the superior 

 maxillary. The second portion of the superior maxillary consists 

 of two fibrous and flexible branches united together, where they 

 are connected to the lateral part of the broadest portion of the 

 central portion, by a moveable ai'ticulation, whence they diverge, 

 the one proceeding to join the lower maxilla at the junction of 

 its dental and articular portions, the other proceeding forwards 

 and downwards to join the inferior maxilla at its symphysis. 

 The bones of the head differed in their structure, but none of 

 them contained ossific matter. 



1. Some were composed of a thin, very flexible, fibrous lamina, 

 presenting numerous ridges on their outer surface, arranged dif- 

 ferently in each. This was the structure of the opercular bones, 

 and of two quadrilateral plates, one on the surface of each cheek, 

 placed immediately behind the anterior margin of the inter- 

 maxillary bone, united to each other by a portion without ridges 

 on its external surface which passed over the dorsum of the 

 snout and covered the anterior portion of the nasal processes of 

 the intermaxillary. A thin and narrow porous layer of this tissue, 

 apparently continued from the opercular bone, passed along the 

 upper margin of the orbit. 



2. Some were composed of a fibrous-looking tissue, either 

 forming flexible plates and bands without any ridges, or masses 

 of greater thickness. The palatine bones and a part of the max- 

 illary bones consisted of thin broad plates, of this texture, while 

 the body of the sphenoid, the anterior sphenoid, the vomer, the 

 intermaxillary, and the central portions of both upper and lower 

 maxillae were formed of thicker masses of the same texture. The 

 lower maxilla contained true cartilage in its interior. 



3. Some were composed of true cartilage enveloped in an ex- 

 ternal layer of a fibrous-looking tissue. This was the structure 

 of the lateral and posterior walls of the cavity of the cranium. 



4. Some were composed throughout of true cartilage, having 

 no fibrous envelope except that constituting the perichondrium. 

 This was the sti'ucture of the anterior frontals, and the portion 

 of cartilage firmly embracing the posterior and middle portions 

 of the nasal processes of the intermaxillary. 



The branchiostegous membrane is short, and contains four 

 short, very flexible and thin branchiostegous rays, besides three 

 others very indistinctly marked placed posterior to these. 



