80 PROFESSOR OWEN ON THE OSTEOLOGY OF 



If a line drawn along the floor of the nostrils be intersected by one drawn parallel 

 with the lower surface of the basioccipital and basisphenoid, an angle of 45° is inter- 

 cepted in the Human cranium ; whilst in the Gorilla, the lower plane of the basioccipital 

 ( 1 ) and basisphenoid ( 5 ) and the plane of the floor of the nostrils ( 20, 21 ) are parallel. 



In the Gorilla the precondyloid canal is relatively smaller than in Man, and, in the 

 present skull, behind the foramen there is on each side a well-marked pit, which is not 

 present in the variety of the Gorilla from the Gaboon, hitherto observed by me. 



The extent of the basisphenoid ( 5 ) is much greater in the Gorilla than in the Papuan ; 

 and, as it is wholly excavated, inflated as it were, by large sphenoidal sinuses ( 5 ), these 

 differ from those in Man in having a stronger, more complete and belter-defined bony 

 floor : the communication with the middle meatus of the olfactory cavity in the Gorilla 

 is by a perforation at the lower part of the anterior wall of the sinus, instead of by a 

 wider and less regular vacuity in the floor of the sinus, as in Man (PI. XXX.). 



In the variety of Gorilla here described, the sinus in the presphenoid (body of the an- 

 terior sphenoid, PI. XXVIII. 9) is distinct from that in the basisphenoid. Absorption 

 and expansive growth have not obliterated the primitive distinction between these 

 bodies of the two middle cranial vertebrae. The two sinuses (5) and (9) communicate 

 with each other at the middle hne, just above their common opening into the nasal 

 meatus. 



The suture between the basioccipital ( 1 ) and basisphenoid ( 5 ) still remains in the 

 adult Gorilla, but all trace of it is obliterated in the Papuan skull compared. 



The absence of any depression for a sella turcica, as well as of postclinoid processes, 

 is very remarkable in the present variety of the Gorilla'. 



The internal meatus (PI. XXVIII. m) is smaller in the Gorilla than in Man, as is also 

 the foramen jugulare below the petrosal. 



The intracranial part of the petrosal (le) is shorter but broader, its upper surface is 

 more level, and more horizontal in position. 



The long axis of the foramen ovale is in the antero-posterior direction, and is not 

 transverse as in Man. 



The interorbital sinuses (/) in the Gorilla are divided from each other in the median 

 plane by a septum of extremely dense bone formed by the backward production of the 

 frontal and of the coalesced median margins of the nasals, forming a plate (15, 11) an- 

 swering to the ' crista ' of Soemmerring, but much larger, thicker, and of denser texture. 

 It is of a triangular form, widening as it descends to an extent of one inch three lines. 

 The posterior margin of the nasal plate is firmly united by a wavy suture to the equally 

 dense interorbital part of the frontal : a small part of the inferior border, near the pos- 

 terior angle of the nasal plate, unites with the ' lamina perpendicularis sethmoidei ' (14). 



The relative position of the nasal and orbital cavities is diflferent in the Papuan and 



' The postclinoid processes exist in the skulls of the variety of the Gorilla from the Gaboon which I have 

 examined, but these variable processes offer no character of consequence. 



