128 



ANATOMY OF VERTEBRATES. 



by the alisphenoid. Thus in the bone 6, we have all the characters 

 of that so numbered in figs. 81, 83, and 85, and called 'ali- 

 sphenoid ' in the fish. The chief modification is due to the greater 

 developement of 3, fig. 90, in Chelonia, which overlaps 6 as well 

 as 2. 



The parietals, figs. 90, 91, are united, as in Cyprinoid and 

 Ganoid fishes, by the sagittal suture, and are much expanded both 

 transversely and longitudinally, overlapping, in the Turtle, the 



91 



Skull of Turtle (Chelone mydas) 



superoccipital, fig. 90, 3, and articulated with it and the mastoids, 

 fig. 91, 8, behind; and with the frontals, ib. n, before. Each 

 parietal, also, sends down a long vertical plate, i' ', fig. 90, which 

 unites with the alisphenoid, 6, and orbitosphenoid, 10, this ossifica- 

 tion taking the place and function of the latter neurapophyses in 

 fishes. 



The bone, figs. 89, 91,8, which articulates with the paroccipital 

 4, parietal 7, and postfrontal 12, which affords the surface of attach- 

 ment to the upper end of the tympanic 28, enters into the for- 

 mation of the acoustic chamber in some Emydians, and projects 

 outward and backward to give insertion to the latissimus colli 

 and trachelomastoideus, repeats the chief and essential characters 

 of the bone so numbered, and called ' mastoid ' in Fishes, figs. 75, 

 76, 83,85,8: and forms the transverse process of the parietal 

 vertebra. 



The forward continuation of the vertebral bodies from 5 remains 

 cartilaginous : the lower half of the sides of the prosencephalon 



