1G0 



ANATOMY OF VERTEBRATES. 



between the nasals, 15. The prefrontal, 14, extends to the nostril, n. 

 The lacrymal, 13, forms the rest of the fore part of the orbit, ex- 

 tending forward upon the face. The sides of the premaxillary, 22, 

 bend abruptly down in front of the nostrils, to join the maxillary, 

 20, 21 ; this forms the lower boundary of the nostril, n, and joins 

 above and behind with the prefrontal, lacrymal, and nasal bones : 

 the maxillary projects below the orbit, like a forward continuation 

 of the zygoma, becomes more prominent as it advances, and soon 

 forms the outer angle of the three-sided socket of the canine tusk, c. 

 There is a single but strong zygomatic arch formed by the malar, 

 26, and squamosal, 27, abutting against the upper end of the tym- 



99 



Skull of Dicynodon 



panic pedicle, 28. The rami of the lower jaw augment in depth 

 from the angle to the symphysis, where they are confluent. The 

 angle projects a very little way beyond the articulation. The 

 articular surface is moderately concave, and looks obliquely up- 

 ward and backward. The elements of the posterior half of the 

 ramus answer to the articular, angular, 26, and surangular, 25. A 

 thin vertical splenial plate, on the inner side of the ramus, begins 

 about an inch in advance of the angle, and extends forward to the 

 symphysis, at the back part of which it appears to become con- 

 fluent with its fellow. The part answering to the angular diverges 

 from the surangular, and forms the hind boundary of an oblong- 

 vacuity at the middle of the side of the ramus, the fore part of 

 which vacuity is formed by a bifurcation of the dentary element, 

 2.3. This is thickened and strengthened by a ridge, subsiding at 

 the vertical channel upon the side of the symphysis, receiving the 



