412 PROFESSOR OWEN ON THE OSTEOLOGY OF 



the mastoidal element developes no continuation of the squamous plate, but the hind 

 border of this plate curves down to the place of the primitive suture between the squa- 

 mosal and mastoid. The whole of the squamosal receives air-cells from the mastoid in 

 the Chimpanzee, and its exterior surface is made convex and, as it were, swollen out by 

 them : no part of the squamosal is so modified in Man*. 



At the first view of the skull of the great Chimpanzee, one is struck by its superior 

 size to the human skuU, especially its greater length, and the greater breadth of the face 

 and of the occiput : the brain-case is made to appear more contracted in proportion 

 than it actually is, by the superaddition of the enormous intermuscular crests and supra- 

 orbital ridge : it would seem, indeed, as if the osseous matter required to form the ex- 

 panded cerebral chamber in the human skull had been here expended in the formation of 

 the great external crests and ridges. Notwithstanding, however, this superiority of size 

 in certain dimensions, and the apparently massive character of the skull of the great 

 Chimpanzee, it is actually lighter than that of Man. The cranium of the adult male 

 Troglodytes Gorilla, figured in Plates LXI. LXII. & LXIIL, weighed 1 lb. 7 oz. 8 drs. 

 avoirdupois, whilst the cranium of a male Australian, without the lower jaw, weighed 

 1 lb. 8 oz. 10 drs. This unexpected result is due to the greater size and extent of the 

 air-cells in the Troglodytes Gorilla. The air introduced from the tympanic chamber 

 into the mastoid extends backwards into cells, continued along the base of the 1am- 

 bdoidal crista to its junction with the parietal ci'ista, and from the mastoid forwards, 

 inflating the whole squamosal plate as far as the alisphenoid, which, with the pterygoids, 

 receives air from the sphenoidal sinuses. 



The upper part of each sphenoidal cell is divided by a plate of bone entering inwards 

 and downwards from the upper and outer wall and folded round the canal continued 

 from the foramen rotundum, and conveying the second division of the trigeminal nerve 

 to the sphenopterygoid fossa. In Man, the canal continued from the foramen rotundum 

 to the back-part of the orbit does not impress the wall or encroach upon the cavity of 

 the sphenoidal sinus. The sphenoidal sinuses communicate, each by a small round 

 aperture, with the back-part of the superior nasal meatus, as in Man. 



The frontal sinuses are divided from each other by a strong median vertical septum, 

 and extend far outwards along the base of the supraorbital crest ; they open below into 

 the middle meatus, as in Man. The great maxillary sinus or antrum is chiefly remark- 

 able for its extension upwards, where it swells out the maxillary contribution to the 

 inner wall of the orbit ; the nasal aperture of the antrum, of a rounded form and two- 

 thirds of an inch in diameter, is covered by the overhanging inferior turbinal bone : the 

 lachrymal canal terminates at the upper part of the orifice of the antrum, not in advance 

 of it, as in Man. 



The osseous parts of the olfactory capsule, which have coalesced with the prefrontals 

 and form the ' superior ' and ' middle ' turbinal processes of the sethmoid, are present, 



* The extension of the auditory cavity into this element of the temporal is found in many Marsupials and 

 Rodents. 



