AND AVES OF NORTH AMERICA. 



wardly it is prolonged, forming the lower margin of the internal fossa, and then passing 

 between the coronoid and articular. A third laminar prolongation extends to beyond 

 even these, between the plates of the splenial. 



The articular is the largest bone behind (be dentary. It is convex externally, and 

 sends a, longitudinal ridge from the cotyloid cavity to that of the coronoid, thus enclosing 

 a, large shallow fossa. 



Fig. 50. 



The accompanying cut represent a section of the ramus, about 

 two inches behind the inferior articulation and some distance be- * JlBllk 



bind the commencement of the coronoid process. It is also near // ^ 



the distal extremity of the subarticnlar and the proximal of the ill 



'{splenial. The two portions of tin- angular 5 and ;7 unite a short if 



distance anteriorly beneath the '{splenial. M 



In the splenial articulation the posterior bone presents the con- rv^^'^^^P 2 



dyloid, the anterior the cotyloid face. The former narrows and re- 4 1111^- 

 treats upwards and backwards. The articulation allows of a ro- 

 tary motion inwards and upwards, the alveolar margin of the den- 

 tary bone being thrown upwards and outwards. Tin's motion 

 is permitted by the laminar character of the overlapping margins 

 of the splenial, etc., as ibllows: 



The principal body of the dentary comes to an obtuse but grooved posterior termina- 

 tion. Its external wall is prolonged more posteriorly, the inferior margin fitting a. rabbet 

 of the outside of the splenial. The superior margin of this thin plate is much lower than 

 the truncate extremity, and its margin gradually rises to meet the outer margin of the latter. 

 The section of the splenial is U-shaped, much thickened at the turn. The inner lamina is 

 more elevated than tin; outer, and is concave, turning outwards above to conform to the 

 dentary. A narrow laminar prolongation of the angular is observed between the folds of 

 the U. An outwardly convex, wedge-shaped terminus of the articular, is included be- 

 tween the inner lamina of the coronoid and the outer lamina of the dentary moving 

 freely on the latter. There is, then, nothing that prevents this from being a complete 

 articulation, except the angular lamina, which is about half a line in thickness, and proba- 

 bly flexible in life. 



The superior margin of the coronoid is convex outwardly, and is not continuous with 

 that; of the dentary, where the elements forming the splenial articulation are in line. 

 When, however, the process of the articulation is properly applied to the dentary, and 

 tin; coronoid and splenial are in line, as they no doubt were under ordinary circumstances 

 in life, the curvature of the upper margin of the ramus is continuous and normal. At 



1 Coronoid. 



2 Articular. 

 :i Subarticular. 

 1 ? Splenial. 

 •"1 and ;V Angular. 



