EXPLANATION OF THE PLATES. 



visible in the present plates, are distinguished by an asterisk prefixed to the let- 

 ters. 



a. Intermaxillary bones. 

 h. Maxillary. 



N.B. It would have been a far more convenient order to have introduced next 

 to these bones, the nasals k Ic, and the lachrymals / i. 

 c. Jugal. 



Bones visible only in the roof of the mouth. 

 r *d. External pterygoids ; not visible in the present Plates. 

 < e. Palatal bones. 

 (. f. Internal pterygoidal processes. 

 *g. Bones considered by M. Cuvier as the great wings of the sphenoid. By insti- 

 tuting a comparison with other oviparous quadrupeds, I have become con- 

 vinced that these correspond with the lamellar bones in the turtle united to 

 the parietal ; and that they are the same parts which are reduced to two cy- 

 lindrical columns in the lacertae : I should therefore be inclined to name 

 them lateral-parietals. They are not visible in the specimens now repre- 

 sented. 



Dismemberments of the frontal bone, 

 r H. Middle frontal. 

 h. Anterior frontals. 

 h'. Posterior frontals. 



N.B. These bones, in the Ichthyosaurus, send a long process forwards be- 

 neath the anterior frontals, — which emerges thence and re-appears in front 

 of the upper part of the orbit, and might without due care be mistaken for 

 a separate bone. See Plate XVII. 

 h'. Post orbital frontal process. 



{I. Lachrymals, or Ossa unguis. ~1 These would have been more properly 

 k. Nasals; J placed next to b, the maxillaries. 



*/. This letter is not appropriated by M. Cuvier. I shall hereafter apply it to 

 the Os petrosum ; which in all oviparous quadrupeds, as indeed in some 

 Mammalia (e. g. the ruminantia), is a separate bone. 

 m. Parietal. I should consider this as the middle parietal, and (as I have before 

 observed) the bones marked g as lateral parietals. 



Dismemberments of the temporal bone. 

 n. Squamoso-zygomatic portion. 

 «'. Mastoid process, — connected with the preceding in the crocodile ; but in most 



other oviparous quadrupeds forming a separate bone. 

 o. Tympanal bone, or Os quadratum. 



N.B. The Os petrosum, to which I have assigned the vacant letter *^, ought 

 here to follow. 

 p." A bone connecting the tympanal bone and the posterior part of the jugal bone ; 

 peculiar, I believe, to the crocodile. 



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