THE SKELETON OF THE VERTEBRATE HEAD. 161 



maxillary palatal plates, and more especially of the ethmoidal 

 neurapophyses, has forced backwards and towards the middle 

 line, not only the bone called " palatal " in the lizard, but also 

 the pterygoids ; and as the latter also exhibit that remarkable 

 tubular development, various phases of which are perceptible 

 in the Chelonians, Birds, and Mammalia, the former again 

 presents the ornithic vomerine aspect. 



In the Ophidia the two halves of the palatal system are 

 widely separated at the middle line. The so-called "palatals," 

 elongated forwards into the ethmoidal region, articulated by 

 ascending processes to the pre-sphenoid, slightly attached 

 externally to the maxillaries, as in the lizards, bound as in 

 these reptiles, the nostrils posteriorly, but do not separate 

 them mesially. 



In the frog, the so-called " palatals " extend transversely 

 outwards from the " os en ceinture " to the maxillaries, being 

 also connected at their outer extremities with the pterygoids. 

 The latter are articulated posteriorly to the post-sphenoid and 

 to the quadrate bone. The " os transversum " has disappeared 

 at the junction of the so-called palatal, pterygoid, and maxillary. 



The modifications presented by these bones in reptiles and 

 Amphibia are much too numerous to be followed in detail at 

 present. I have therefore selected those which are essential 

 for the elucidation of my subject ; and shall sum up the con- 

 clusions I draw from them, by a comparison of them with the 

 corresponding elements in chelonians. 



The chelonians, we are told, have no "transverse bone." 

 They are distinguished in this respect from all the other 

 reptiles. But if we examine the skull of a tortoise, we shall 

 find all the elements which enter into the formation of the 

 palatine aspect in that of the crocodile. In front are the 

 intermaxillaries, immediately behind which, in the median 

 line, is the double bony plate, which is usually described and 

 figured as the fore part of the so-called " vomer," but to which 



If 



