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parietal and a portion of the mastoid (), and unites anteriorly with the descending lateral plate 

 of the parietal bone. 



The parietal (7) is a large and long, symmetrical roof-shaped bone, with a median longitu- 

 dinal crest along its upper surface, where the two originally distinct moieties have coalesced. 

 It is narrowest posteriorly, where it overlaps the superoccipital, and is itself overlapped by 

 the mastoid : it is convex at its middle part on each side the sagittal spine, and is continued 

 downwards and inwards, to rest immediately upon the basisphenoid. This part of the parietal 

 seems to be formed by an extension of ossification along a membranous space, like that which 

 permanently remains so in the Frog, between the alisphenoid and orbitosphenoid : the mes- 

 encephalon 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 

 anterior border of the lateral plate of the parietal and the posterior border of the correspond- 

 ing plate of the frontal. 



The frontals (11) rest by descending lateral plates, representing connate orbitosphenoids, 

 upon the attenuated, 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 superorbital 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 pre- 

 sphenoid below, the prefrontals and nasals before, and the superorbitals at their lateral mar- 

 gins. 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 frontal, forming a septum between the olfactory pro- 

 longations 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 (is) is a moderately long trihedral bone, articulated by its expanded cra- 

 nial 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 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) 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 (u) are connate with the lachrymals (rs). 



