44 



ANATOMY OF VERTEBKATES. 



97 



The exoccipitals, figs. 26 and 27, 2, contributing somewhat 

 more to the occipital condyle than in the Crocodile, develope, as 

 in that reptile, the paroccipital, figs. 27 and 28, 4, as an out- 

 standing exogenous ridge or process : but it is lower in position 

 than in the Crocodile (vol. i. p. 135, fig. 93). The superoccipital, 



figs. 26,27, 28, 3, as compared with 

 that of the Crocodile, ib., mani- 

 fests more strongly the flattening 

 and developement in breadth, by 

 which the spinous elements lose 

 the formal character from which 

 their name originated, and are 

 converted from long into flat 

 bones. It always protects the 

 cerebellum ; is absent in the Frog, 

 where this organ is a mere rudi- 

 ment ; and is present in the Cro- 

 codile in the ratio of the superior 

 size of the cerebellum. The fur- 

 ther developement of the cere- 

 bellum is the condition of the 

 superior breadth of the spine or 

 crown of the epencephalic arch, 

 fig. 26, N I, in the Bird. 



Of the three bones above de- 

 fined, 2 is developed in the back 

 part of the cartilage inclosing the 

 ear-capsule, and all bear the same 

 relation thereto, in the primordial 



cranium. 



as Nos. 1, 2, 3, 4j 



m 



(P 



Base of skull, Ostrich. Clieloiiia (p. 131, fig. 92), aud 



as Nos. 1, 2, 3, in the Crocodile 

 135, fig. 93). No. 2, in the Bird, as in the Crocodile, in- 

 cludes, connately developed therewith, the bone 4, in the Emys. 

 A basal view of the epencephalic arch is given in the young 

 Ostrich, fig. 27, showing the proportions in which the centrum, 

 \x, the neurapophyses 2, 2, and the neural spine, 3, enter into the 

 formation of the neural canal or ^foramen magnum,' 1. The 

 connate element, 4, stands out, like 4 in figs. 81 and 92, as the 

 transverse process of the neural arch. 



The second segment of the skull has for its central element 

 a bone, figs. 26, 27, 5 (basisphenoid), ossified, like some trunk- 



