408 PROFESSOR OWEN ON THE OSTEOLOGY OF 



to the crucial ridge or spine of the human convex occiput, except, in some skulls, the 

 vertical ridge dividing the great subconcave expanse. 



The basisphenoid (5), besides its non-confluence with the basioccipital, has a larger 

 extent uncovered by the vomer and by the bases of the anchylosed alisphenoids ( 6 ) and 

 pterygoids (24) : it is excavated by large sinuses extending into both the alisphenoids 

 and pterygoids : the sinuses are confined to the basisphenoid and presphenoid in Man. 



The broader pterygoids in the Chimpanzee anchylose with and, as it were, embrace a 

 greater part of the base of the ahsphenoid : the foramen ovale {t r) is more remote from 

 the foramen caroticum, and is pushed by the broad ectopterygoid (25) further back 

 from the pterygomaxillary fissure {sp) : the extent of the basis cranii between the 

 carotid foramen and sphenomaxillary fissure being twice that in Man. The styliform 

 process (es) is less developed, and the inner border of the glenoid cavity {g) of the 

 squamosal abuts against its whole length, or even extends below or beyond it. 



Outside the pterygoid the alisphenoid ( 6 ) becomes narrower, and is continued more 

 directly upwards into the temporal fossa than in Man : the ectopterygoid ridge (25) is 

 less developed, and the fossa on the outer side of the ectopterygoid is not present, or is 

 very feebly developed. The alisphenoid contracts instead of expanding as it rises, 

 terminates before it gains half the height of the orbit, and is excluded from junction 

 with the parietal by the meeting of the squamosal with the frontal. The expanded spine 

 (PI. LXI. 7 ) of the parietal vertebra is thus entirely separated from its neurapophyses 

 (e) in the Chimpanzee. In the Australian the alisphenoid ascends higher than the 

 malar, but not so far as in the European. Besides the relatively smaller size of the 

 parietal bones, the early obhteration of the sagittal suture, and the development of the 

 crista upon it, the lower border of the parietal is straighter than in Man and more 

 equally divided between the squamosal and the mastoid. The diploe is obliterated at 

 the middle of each parietal in the Chimpanzee. 



The presphenoid, where it forms the seat of the optic chiasma, is not defined, as in 

 Man, by the abrupt excavation of the sella behind it ; but the sphenoidal cells raise the 

 floor of the sella to a level with the chiasmal platform into a convexity which gradually 

 sinks as it recedes into the hollow of the sella, which is shallower than in Man, and the 

 longitudinal diameter is greater than the transverse one. If the sella or space between 

 the anterior and posterior clinoid processes be divided into a convex chiasmal and a 

 concave pituitary part, these are more equal in the Chimpanzee than in Man. 



The orbitosphenoids coalesce nearer their origin with the orbital plates of the ali- 

 sphenoid, obliterating the fissure which in Man is continued outwards from the ' fora- 

 men lacerum anterius ;' so that this foramen is better defined and has a subquadrate 

 form in the Chimpanzee ; and there are no ridges, called ' lesser alse,' defining the fossa 

 of the anterior lobe from that of the middle lobe as in Man. The suture between the 

 orbitosphenoids and the frontals is quite obliterated in the Chimpanzee. A short 



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