REMAINS OF REPTILES AND FISHES. 105 



articular process, and is probably nothing more than a prolonga- 

 tion of the angular bone. 



This styliform process has been described as the entire man- 

 dibular ramus in some of the Acanthodei, and is seen occasion- 

 ally attached to the head, the dentigerous bone, with the teeth, 

 having been detached. In Sir P. Egerton's figure of A. Wardi 

 these styliform bones, so denuded, are seen still articulated to 

 the head and thrown backwards ; the teeth are frequently found 

 attached to the thin-walled dentigerous bone, the styliform pro- 

 cess having probably been left so attached to the head. 



The teeth are never found separated from the bone. There 

 are five or six in each ramus, two of the larger being in the 

 centre, the smaller ones in front and behind ; they are com- 

 pressed in the direction of the jaw, and when seen in this posi- 

 tion they have the shape of as many equilateral triangles with 

 the lateral margins a little hollowed towards the apices, which 

 are recurved ; they are expanded at the base, where they be- 

 come confluent, and are coarsely and irregularly striated from 

 one extremity to the other ; and the surface being liable to ero- 

 sion, the striation is frequently exaggerated. 



The upper jaw is co-extensive with the mandible, and is ap- 

 parently formed of one piece. The teeth are like those of the 

 under jaw, and lock very accurately into them ; they are of the 

 same size and character, and are equal in number to those of 

 the mandible. The largest teeth are nearly ith of an inch in 

 length ; they are much wider than they are thick from back to 

 front. 



On making a longitudinal section of the teeth in the direction 

 of the jaw, the structure is found to be very peculiar. The jaw 

 itself is composed of very dense bone on the surface, in which 

 the Haversian canals are well defined, and the radiating cells 

 are very numerous and minute ; they are elongated fusiform, 

 with the canaliculi (when observable) sufficiently abundant, and 

 arranged for the most part at right angles to the long axis of the 

 cells. In the superficial and denser portions of the tissue the 

 cells and tubules are the most minute ; in the deeper portions 

 they are larger and less regular in form, and the bone becomes 



