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 better-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 (Pl. XXX.). 
In the variety of Gorilla here described, the sinus in the presphenoid (body of the an- 
terior sphenoid, Pl. 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 vertebree. The two sinuses (5) and (9) communicate 
with each other at the middle line, 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 (Pl. 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 (16) 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 (f) 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 ethmoidei’ (14). 
The relative position of the nasal and orbital cavities is different 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. 
