STRUCTURE OF THE SKULL OF THE PYTHON. 79 



of ossification along a membranous space, like that whicli 

 permanently remains so in the frog, between the alisphe- 

 noid and orbitosphenoid : the mesencephalon and the chief 

 part of the cerebral lobes are protected by this unusually 

 developed spine of the mesencephalic vertebra. The 

 optic foramina are conjugational ones, between the ante- 

 rior border of the lateral plate of the parietal and the 

 posterior border of the corresponding plate of the frontal. 

 The frontals, 11, rest by descending lateral plates, re- 

 presenting connate orbitosphenoids, 12, upon the attenu- 

 ated, pointed prolongation of the basisphenoid : the upper 

 surface of each frontal is flat, subquadrate, broader than 

 long in the boa, and the reverse in the python, where the 

 roof of the orbit is continued outwards by a detached super- 

 orbital bone: there is a distinct, oval, articular surface near 

 the anterior median angle of each frontal to which the 

 prefrontal is attached : the angle itself is slightly produced, 

 to form the articular process for the nasal bones. The 

 smooth orbitosphenoid plate of the frontal joins the outer 

 margin of the upper surface of the frontal at an acute 

 angle; the inner side of each frontal is deeply excavated 

 for the prolongation of the cerebral lobes, and the cavity 

 is converted into a canal by a median vertical plate of 

 bone at the inner and anterior end of the frontal. The 

 frontals join the parietals and postfrontals behind, and, 

 by the anchylosed orbital plates, the presphenoid below, 

 the prefrontals and nasals before, and the superorbitals at 

 their lateral margins. The orbitosphenoids have their 

 bases extended inwards, and meet below the prosence- 

 phalon and above the presphenoid, as the neurapophyses 

 of the atlas meet each other above the centrum. The 

 anterior third part of such inwardly-produced base is met 

 by a downward production of the mesial margin of the 



