THE SKELETON OF THE VERTEBRATE HEAD. 159 



groove, which is applied against the under surface of the 

 acuminated anterior extremity of the post-sphenoidal centrum, 

 which is therefore interposed between it and the pre-sphenoidal 

 centrum. This bone, more or less compressed or extended 

 laterally, separates the posterior nostrils from one another. 

 Its anterior extremity reaches the anterior limits of these 

 orifices, or, passing forwards into the palate between the 

 ethmoidal neurapophyseal and maxillary palatal laminse, and 

 concealed more or less by them, may terminate on the surface 

 of the palate between the intermaxillary palatal plates. When 

 this bone is much compressed it is single throughout ; when 

 flattened, it is more or less extensively divided in the 

 mesial line. 



The palate-bones of the bird, more or less elongated, 

 extend anteriorly under the maxillary palatal lamina, to 

 which in general they are only slightly connected, forward to 

 the intermaxillary palate-plates, with which they are anchylosed 

 or articulated, separated from one another in front, to form the 

 lateral boundaries of the posterior nares, the palate-bones 

 become broader posteriorly, approach one another, and are 

 either attached to, or anchylosed with, the posterior extremity 

 of the so-called "vomer." Their posterior extremities are 

 provided with facets for articulation with the bar-like ptery- 

 goids, which extend from them, outwards and backwards, to 

 articulate with the quadrate bone on each side. The pterygoids 

 of certain birds have also secondary connections ; they 

 articulate with processes which project from the post-sphenoidal 

 centrum in some part of its extent ; and on which their shafts 

 glide, rotate, or vibrate. 



The reciprocal relations of the so-called "vomer," the 

 palatines, and pterygoids of the bird, are extremely interesting 

 and important. At present, I can only direct attention to 

 those relations which bear upon my subject. When the 

 palate-bones are greatly developed, the "vorner" diminishes. 



