78 



VERTEBRATE SKELETON 



followed on the medial side by one or more splint-like bones, the 

 splenials (opercnlare) which, with the dentaha, are the only tooth 

 bearing bones in the lower jaw. On the lower margin of the jaw, 

 and extending up on either side and reaching back almost to the angle 

 of the jaw, is an angulare with a sur (supra) angiilare dorsal to it. 

 At the point where most of the occludent jaw muscles are attached 

 a coronoid (complementare) bone is developed (and in Teleosts a 

 'sesamoid articulare' may appear at the insertion of the muscles). 

 On the medial and ventral side of the posterior part of the Meckelian 

 and the articulare is a goniale (derm- or autarticulare) which usually 

 fuses with the articulare. Of all of these membrane bones of the 

 lower jaw, dentale, angulare and splenial are the most constant as 

 separate elements. 



Fig. 8i. — Lower jaw of Lacerta (Gaupp, 'ii). A, outer and B, inner side ot jaw of 

 47 mm. embryo; C, outer and D, inner side of adult jaw. a, articulare; an, angulare; c, 

 coronoid; d, dentale; g. goniale; q, quadrate; s, splenial; 5a, surangulare. 



The Skull in Separate Classes 



CYCLOSTOMATA.— The Cyclostome skull never passes the 

 cartilage stage, but several kinds of cartilage — true and pseudo, 

 hard and soft — ^are described in it. The skulls are pecuhar and many 

 parts are not readily homologised with those of other Vertebrates, 

 and there is difficulty in comparing all details of Myxinoid and Petro- 

 myzontid skulls. 



