160 ON THE MORPHOLOGICAL CONSTITUTION OF 



When, again, the "vomer" is much developed, the palatines 

 are in an atrophied condition. The pterygoids present phases 

 of development dependent on the variations of the palatines 

 and pterygoids. The two extremes may be observed in the 

 parrots and the struthious birds. In the former, the palatines 

 are enormously developed, while the "vomer" has disap- 

 peared. In the latter, the " vomer " is greatly elongated and 

 developed, while the palatines present the relation, and ex- 

 hibit the form, of the " transverse" or " adgustal " bones of 

 the reptile. 



The Palatal Arch and the Pterygoids in Reptiles and 

 Amphibians. The three bones on each side, which form the 

 palatal system of the ordinary lizard, present the same 

 relations, and almost the same form, as the " vomer," palatines, 

 and pterygoids of the struthious birds. The pterygoids are 

 in every respect similar. The " transverse bones " of the 

 lizard are also, in relations and almost in form, like the 

 palatines of these birds. The so-called " palatals" of the 

 lizard, while they exhibit all those relations to the " transverse" 

 and pterygoids, which the "vomer" of the bird presents, 

 differ from that double bone in this respect, that although in 

 contact at the mesial line, they are comparatively so much 

 broader, occupying so much of the comparatively narrow 

 palatal space that they touch the maxillaries by their anterior 

 external angles. They bound, therefore, the internal nares 

 posteriorly ; but, like the so-called vomer in the bird, separate 

 them from one another, passing forward like that double bone 

 to the ethmoidal neurapophyseal plates, which constitute the 

 so-called " vomer " of the lizard. In the monitors, these so- 

 called " palatines," like the pterygoids, are evidently separated 

 in the middle line, and forced backwards along the inner 

 margin of the maxillary towards the transverse bones, by the 

 development and elongation of the ethmoidal neurapophyseal 

 elements. In the crocodiles, again, the full development of 



