410 PROFESSOR OWEN ON THE OSTEOLOGY OF 



The air-cells, which are confined to the mastoid in Man, extend in the Chimpanzee 

 into the squamosal, inflating it above the base of the zygomatic process, and as far 

 forwards as its junction with the frontal, where the squamosal sinuses are contiguous 

 to, though they seem not to communicate with, those of the alisphenoid. 



The petrosal (PI. LXIII. p j, lo) is larger in the Chimpanzee than in Man ; its antero- 

 posterior diameter especially is greater : its eustachian process (e) * is much more deve- 

 loped and more distinct from the proper apex (le) of the petrosal, which is less jagged 

 than in Man, and rests more completely upon the base of the alisphenoid, almost filling 

 up the vacuity called ' foramen lacerum medius ' in Man. The carotid foramen (c) is 

 smaller than in Man ; it is defended by an angular ridge {v) externally, which divides 

 it from the stylohyal fossa (as) in the Chimpanzee, and is the sole representative of the 

 vaginal process : the prejugular [pj) process from the inner side of the foramen caroticum 

 abuts upon a corresponding process of the basioccipital, and with it forms the anterior 

 boundary of the foramen jugulare {j). 



The intracranial part of the petrosal is relatively shorter in the Chimpanzee than 

 in Man : its upper surface is more even : the channel of the lateral sinus which defines 

 it behind is narrower. The foramen auditorium internum has not the overhanging 

 ridge ; the superior ridge is not grooved by the petrosal sinus. 



The chief characteristics of the frontal, due to its smaller size and the supraorbital 

 ridge, have already been noticed : besides these deviations from the human type, the 

 ectorbital processes stand further out before they bend down to join the malar, and the 

 postorbital angles descend much lower into the temporal fossa and form a longer wedge 

 between the alisphenoid and malar bones, the point terminating on a level with the 

 floor of the orbit. 



The vomer (is) is deeper and more oblique than in Man, and does not reach so far 

 forwards. 



The coalesced prefrontals {lamince media ccthmoidei) are connate, as in Man, with the 

 olfactory capsules forming the sethmoidal cells, the superior turbinals, the ' partes 

 planse ' and the cribriform plate, but they do not extend backwards to form a ' crista 

 galli.' The cribriform plate is much smaller, and is sunk into a deep (rhinencephalic) 

 fossa. 



The palatines (20) form a smaller proportion of the bony palate ; their mesial ante- 

 rior ends advance forwards in a point between the maxillaries, but the mesial posterior 

 ends, which project backwards in a point in Man, are truncate, and the border of the 

 bony palate there presents either a shallow median emargination, between two slighter 

 ones, or the whole posterior boundary (in the younger male) is slightly undulated with 

 a general curve concave backwards ; whilst in every variety of the human race the 

 same border presents two lateral concave emarginations divided by the median point. 

 The posterior palatine foramina (20) are close to the anterior palato-maxillary suture : 



* This process may belong to the tympanic rather than to the petrosal. 



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