150 ANATOMY OE VERTEBRATES. 



Ijetween tlie olfactory prolongations of the brain, but is not con- 

 fluent with the frontal septum: the outer portion of the orbitosphe- 

 noidal jilate is smootli externally, and deeply notched posteriorly 

 for the optic foramen. 



The post-frontal, fig. 97, 4, is a moderately long trihedral bone, 

 articulated by its exjianded cranial end to the frontal and parietal, 

 and l)ent down to rest upon the outer and fore angle of the ecto- 

 pterygoid, 25. It does not reach that l^one in the Boa, nor in 

 poisonous Ser2ients. In both the Boa and Python it receives the 

 anterior sharp angle of the parietal in a notch. 



The natural segment which terminates the cranium anteriorly, 

 and is formed by the vomerine, prefrontal and nasal bones, is very 

 distinct in the Ophidians. 



The vomer is divided, as in some ganoid Fishes and Batrachians, 

 but is edentulous : each half is a long, narrow plate, smooth and 

 convex below, concave above, with the inner margin slightly 

 raised : pointed anteriorly, and with two processes and an inter- 

 vening notch above the base of the pointed end. The prefrontals, 

 14, are connate with the lacrymals. The two bones which inter- 

 vene between the vomerine and nasal bones are the turbinals, fig. 

 96, d, they are Ijcnt longitudinally outwards in the form of a 

 semicylinder about tlic termination of tlie olfactory nerves. 



The spine of the nasal vertebra is divided symmetrically as in 

 the Frog, forming the nasal bones, fig. 97, 15 ; they are elongated, 

 licnt plates, with the shorter upper part arching outward and 

 downward, completing the olfactory canal above ; and with a longer 

 median plate forming a vertical wall, aj)plied closely to its fellow, 

 exccjrt. in front, where the nasal process of the premaxillary is 

 received in the interspace of the nasals. 



The acoustic capsule remains in great part cartilaginous : there 

 is no detached centre of ossification in it : to whatever extent this 

 capsule is ossified, it is by a continuous extension from the alisphe- 

 noid. The long stapes, fig. 97, 16, extends from the ' fenestra vesti- 

 buli ' to the subcutaneous ear-drum attached to the tympanic bone, 

 28. The sclerotic capsule of the eye is chiefly fibrous, witli a thin 

 inner layer of cartilage ; the olfactory capsule is in a great measure 

 ossified, as above described. 



MaxiUary arch. — The palatine, fig. 96, 20, or first piece of this 

 arch is a strong, olilong bone, having the inner side of its obtuse 

 anterior end applii'd to the sides of the prefrontals and turbinals, 

 and, near its posterior end, sending a short, thick process upward 

 and inward for ligamentous attadunent to the lacrymal, and a 

 second similar process outward as the point of suspension of the 



