785 



to greater bulk or activity of muscles, and not to be explained by the operation of external 

 circumstances favouring greater general development of size and power. 



Comparison of the Skull of the male Troglodytes Gorilla with that of a male Negro. 



In the side view the most remarkable difference is the small proportional size of the cra- 

 nium, as defined by the superorbital ridge and the zygomatic arch from the facial part of the 

 skull, in the Gorilla ; notwithstanding the presence of the strong sagittal and lambdoidal 

 cristse which are superadded to the cranial part of the skull, and prolong its extent upwards 

 and backwards beyond the proper walls of the brain-case in this great Ape. The temporal 

 ridge, arching upwards and backwards, and blending with its fellow to form the parietal crest, 

 defines the upper contour of the cranium in the Gorilla, the intercepted part of the frontal 

 sinking below the converging ridges and forming a concavity in their interspace. In Man the 

 frontal swells out into a broad convexity between those ridges, which are feebly defined by the 

 slight subsidence of the muscular temporal surface below the level of the rest of the frontal, 

 and this indication of a ridge usually disappears before it reaches the coronal suture, where 

 nearly the whole upper surface of the cranial dome intervenes between such indications. The 

 rudiment of the lambdoidal ridge in Man curves with the convexity upwards below the suture 

 to terminate in the occipital spine or tubercle, a free tract of bone more than an inch in 

 breadth dividing the lambdoidal from the temporal ridges, and being continued between them 

 upon the mastoid process. In the Gorilla the enormous lambdoidal crest, blended with the 

 back part of the temporal ridge, curves with the concavity upwards, as it extends from the 

 mastoid, obliterating the suture, to join the hind end of the sagittal crest ; and the lam- 

 bdoidal crest terminates the contour of the cranium behind as the sagittal crest does above. 

 In Man the parietal dome rises high above, and the occiput swells out below, the rudiment- 

 ary lambdoidal ridge ; whilst the larger and longer mastoid process, projecting downwards 

 and extended forwards beneath the meatus auditorius extemus, supports the vaginal plate of 

 the tympanic or auditory process : but in the Gorilla the tympanic or auditory process, pre- 

 senting the form of a semicylindrical tube, is wholly in advance of the shorter mastoid pro- 

 cess, and has no vaginal process at its outer end. The postglenoid process of the squamosal 

 (middle root of the zygoma) is relatively thicker and longer, but more obtuse in the Gorilla. 

 The zygoma is not only much stronger, but the squamosal and malar portions have different 

 forms and proportions in the Gorilla ; the squamosal is as deep and as long as the malar part, 

 instead of being shallower and longer as in Man ; and its upper border rises in the Gorilla 

 into an angular form : the malar portion is accordingly longer, and does not decrease in 

 depth after leaving the body of the bone as in Man. The posterior border of the frontal 

 process of the malar is slightly concave or nearly straight in the Gorilla ; it forms a strong 

 sigmoid curve in Man, convex backwards at its upper half. The superorbital ridge projects 

 very slightly beyond the slope of the frontal between the external angle and the prominent 

 sinus even in the lowest Negro or Australian skull : the prominence of the whole super- 

 orbital ridge, which is the characteristic of the genus Troglodytes, reaches its maximum in 

 the present great species, and forms a well-marked distinction in the comparison of its skull 

 with that of Man. The interorbital part of the ridge, however, projects more suddenly 

 over the root of the nasal in the Ethiopian and especially Australian skulls than in the 



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