80 STRUCTURE OF THE SKULL OF THE PYTHON. 



frontal, forming a septum between the olfactor}^ prolonga- 

 tions of the brain, but is not confluent with the frontal 

 bone : the outer portion of the orbitosphenoids ascends 

 obliquely outwards, and is confluent with the under part 

 of the frontal ; it is smooth externally, and deeply notched 

 posteriorly for the optic foramen. 



The post-frontal, 12, is a moderately long trihedral bone, 

 articulated by its expanded cranial end to the frontal and 

 parietal, and bent down to rest upon the outer and fore 

 angle of the ectopterygoid. It does not reach that bone 

 in the boa, nor in poisonous serpents. In both the boa 

 and python, it receives the anterior sharp angle of the 

 parietal in a notch. 



The natural se2:ment which terminates the cranium an- 

 teriorly, and is formed by the vomerine, prefrontal, and 

 nasal bones, is very distinct in the ophidians. 



The vomer, 13, is divided, as in salamandroid 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 intervening notch above 

 the base of the pointed end. The prefrontals, 14, are 

 connate with the lachrymals, 73. The two bones which 

 intervene between the vomerine and nasal bones are the 

 turbinals, 19; they are bent longitudinally outwards in 

 the form of a semicylinder about the termination of the 

 olfactory nerves. 



The spine of the nasal vertebra is divided symmetri- 

 cally, as in the frog, forming the nasal bones, 15 ; they are 

 elongated, bent plates, with the shorter upper part arching 

 outwards and downwards, completing the olfactory canal 

 above, and with a longer median plate, forming a vertical 

 wall, applied closely to its fellow, except in front, where 



