230 THE VERTEBRATE SKELETON. 



The premaxillae (figs. 38 and 39, 15) are a pair of very 

 small bones forming the floor of the anterior narial opening, 

 they are wedged in between the two maxillae, and send back 

 processes which meet the vomer and palatines. 



The palatines (fig. 39, 10) are a pair of small bones firmly 

 united with the pterygoids behind, with the maxillae and jugals 

 externally, and with the vomer in the middle line. Each also 

 gives off a palatine plate which unites with the expanded lower 

 edge of the vomer, and forms the ventral boundary of the pos- 

 terior nares. Anteriorly the palatines form the posterior bound- 

 ary of a large foramen through which the ophthalmic branches 

 of the fifth and seventh nerves pass to the olfactory organs. 



The pterygoids (fig. 39, 9) are a pair of large bones which 

 unite with one another by a long median suture. They are 

 united also with the palatines in front, and with the quadrate, 

 basisphenoid, basi-occipital, and exoccipitals behind. Each 

 also sends dorsal wards a short alisphenoid plate which 

 meets that from the parietal. 



Piercing the posterior end of the pterygoid is the prominent 

 opening of the carotid canal; a bristle passed into this hole 

 emerges through a foramen lying between the pro-otic and the 

 alisphenoid process of the pterygoid. 



(2) THE LOWER JAW OR MANDIBLE. 



The mandible consists of one unpaired bone, formed by 

 the fusion of the two dentaries, and five pairs of bones, called 

 respectively the articular, angular, supra-angular, splenial 

 and coronoid. 



The fused dentaries (fig. 38, 12) form by far the largest of 

 the bones ; they constitute the flattened anterior part of the 

 mandible, and extend back below the other bones almost to 

 the end of the jaw. 



The coronoid is the most anterior of the paired bones, it 

 forms a prominent process to which the muscles for closing 

 the jaw are attached. 



