78 PROFESSOR OWEN ON THE OSTEOLOGY OF 



basi-facial' (O — O) method, without a corresponding difference really existing between 

 the proportions of the cranium to the face in the two species. The only true mode of 

 demonstrating these relative proportions is by a vertical section through the median 

 line of the skull. This section demonstrates not only the true proportion of the brain- 

 chamber to the rest of the skull, but many other differences of structure, not otherwise 

 appreciable, between the lowest races of Man (PI. XXX.) and the highest species of 

 Ape (Pis. XXVIII. and XXIX.). 



In the Negro and Papuan (Pi. XXX.) the area of the cavity of the nose, as exposed 

 by this section, including therein the sphenoidal and other sinuses, communicating 

 with the nasal passages, equals about one-fourth of the area of the cavity of the cranium. 

 In the Gorilla (PI. XXVIII.) it is very nearly one-half: it is somewhat less in the Orang 

 (PI. XXIX.), owing chiefly to the smaller extent of the interorbital sinuses. The cranial 

 cavity is lower in proportion to its length and breadth in the Gorilla than in the Orang : 

 the vertical line from the lower border of the occipital condyle to the parietal vault 

 above, measures — 



In. Lines. 

 In the Papuan Negro 5 7 



In the Gorilla 3 7 



In the Orang 3 10 



The most anterior part of the cranial chamber is formed by the narrow, deep and 

 well-defined rhinencephalic fossa (rh) in the Gorilla (PI. XXVIII.), but in the Papuan 

 (PI. XXX.) the prosencephalic compartment is continued two-thirds of an inch in advance 

 of the rhinencephalic fossa (rh), and it expands into a much higher and wider arch above 

 it. The rhinencephalic fossa is so slightly depressed and so ill-defined in Man that it 

 has failed to be recognized under any distinctive name in Human Anatomy, although 

 the parts which it contains, as e. g. the ' cribriform plate,' the ' crista galli ' and the 

 ' foramen caecum,' have been duly noted. The distinct definition of this primary divi- 

 sion of the cranial chamber in the Gorilla forms one of the well-marked differences 

 between it and Man. Its antero-posterior diameter is less by one-third than in Man, 

 and the median ridge called ' crista galli ' is rudimental or absent. Another equally 

 strong distinction is seen in the relation of the plane of the cribriform floor of the 

 rhinencephalic fossa with the plane of the upper surface of the basioccipital ( i ) and 

 basisphenoid ( 5 ). In Man the latter ( 5 ) , terminating above in the postclinoid process, 

 forms an angle of 95° with the cribriform plate (rh) ; in the Gorilla they are nearly on 

 the same parallel. 



There being no posterior clinoid process, nor any depression marking a ' sella turcica' 

 in the bisected cranium of the Gorilla, here described, the floor of the cavity of the 

 cranium extends from the foramen magnum straight forwards and a little upwards to 



' In this method the horizontal line is drawn from the lower border of the foramen magnum to that of the 

 fore part of the preniaxillary bone. 



