110 The Rev. W. D. Conybeare's Additional Notices 



ceives a much greater developemcnt*. — Hence also the coronoid process, the 

 use of which is to receive the main action of the temporal muscle, can hardly 

 be said to exist at all in the crocodile ; while on the other hand, an oval hole 

 is formed in those parts of the lower jaw that give attachment to the mas- 

 seter, in order to afford a more powerful adhesion. For this purpose, across 

 the oval hole is stretched a strong fibrous membrane, into which, on the 

 outside, are inserted the fibres of the masseter ; — and on the inside those 

 of the pterygoid, and internal portions of the imperfectly-formed temporal 

 muscle f. 



In the other lacertae, — where the temporal muscle is the great motor of the 

 lower jaw, and the masseter has only its ordinary functions, — the coronoid pro- 

 cess is of considerable extent, being formed by a long process of the crescent- 

 shaped bone ; and there is no large oval hole, but only a sinus in its place, 

 for the insertion of the masseter. 



Now the ichthyosaurus appears to possess an intermediate structure in these 

 respects : for although the oval hole, which characterizes the crocodile, is 

 wanting (being represented only by a sinus in the coronoid), yet the coronoid 

 process itself appears to be far less developed than in the other lacertae, al- 

 though more so than in the crocodile. It appears also to be formed entirely by 

 a process of the coronoid bone, not by the crescent-shaped bone ; although this 

 latter exists on the inner side of the jaw. I am not, however, able to speak with 

 certainty of the termination of the coronoid process, or of the exact outline of 

 the crescent-shaped bone ; all the specimens which I have seen having been 

 obscure in these parts. I would particularly refer to fig. 14. PI. XVI. which 

 represents the interior of the lower jaw in the specimen exhibited at large in 

 fig. 8. of the same plate. The bones are here distinguished by the letters 

 employed throughout these papers, s represents the crescent-shaped bone ; 

 but its outline is much concealed by investing pyrites. Above x there appears 



* I have to acknowledge my obligations to 'a friend, for many of these observations on the parts 

 connected with the temporal and masseter muscles. 



+ These characters belong generally to all the recent species of crocodile ; but in the fossil 

 species described by M. Cuvier, the oval hole was wanting (see his memoir on fossil crocodiles, 

 p. 20.) ; and in all the fossil species of this genus which I have myself examined, the temporal 

 fossae were much more developed than even in the recent gavial. I am persuaded, from every 

 circumstance, that a much nearer approximation to the structure of the other Lacertian genera 

 will be found in the fossil, than in the recent crocodiles : interesting links in the chain of Saurian 

 animals will be thus supplied; and it will probably be found that many of the points in which the 

 ichthyosaurus differs from the recent type, arc only instances of its agreement with the fossil. 



