174 ON THE STRUCTURE OF THE SKULL. 



narrow in front of the orbits and end in a point beyond the 

 nostrils, and bnt a short distance from the extremity of the 

 snout. The supra-occipital lies between, and separates two other 

 comparatively small and insignificant bones (Pa.), which are 

 situated between the posterior edges of the parietals and the 

 epiotics, and, strictly speaking, do not enter into the roof of the 

 cranial cavity at all. Of these two pairs of bones, the anterior 

 represent the frontals of Man, and the posterior his parietals. 

 The position and proportions of the bones are, indeed, remark- 

 ably altered ; but we shall find by and by, that these very vari- 

 able cranial elements undergo almost as great changes of propor- 

 tion and relation even within the limits of the Mammalian class. 



The three bones which correspond with the pars petrosa and 

 pars mastoidea have already been identified. In Man another 

 element, the squamosal, situated above and external to the 

 pro-otic and opisthotic enters into the composition of the tem- 

 poral bone. In the Pike there is a corresponding bone, which 

 forms the external and posterior angle of the skull, and lies 

 above and external to the pro-otic and opisthotic, being usually 

 anchvlosed with the latter. The under and outer surface of this 

 squamosal bone contributes towards the formation of the articular 

 facet for the suspensory apparatus of the lower jaw. There 

 appears to be no ossification in the ethmoidal cartilage, which 

 answers to the lamina perpendicular is of the ethmoid. But, 

 separating the orbits from the nasal chambers, there is on each 

 side of the frontals, and partially overlapped by them, a bone 

 which helps to bound the hinder wall of the nasal chamber, 

 which lies external to the olfactory nerve, and which is in imme- 

 diate relation w 7 ith the nasal division of the trigeminal nerve. 

 This is the bone termed " pre-frontal " by Cuvier, and it obviously 

 corresponds with the lateral mass of the ethmoid in Man, which, 

 in like manner, enters into the wall of the olfactory chamber, lies 

 external to the olfactory nerves, and is traversed by the nasal 

 division of the fifth. 



Thus far the bones entering into the composition of the Pike's 

 cranium (with the exception of the " parasphenoid ") have been 

 identified without much difficulty with those met with in Man. 

 Put there remain several others which seem to be without human 



