THE GREAT CHIMPANZEE. 407 



being convex beconaes concave, expanding into a broad base formed by the supraorbital 

 ridge in front and by the lambdoidal crest behind, continued into the zygomatic arches 

 at the sides. The small cranial dome also supports the strong sagittal crest which at 

 the coronal suture divides and diverges, curving outwards to the external angles of the 

 supraorbital ridge. 



No quadrumanous animal, and few other mammals, offer a greater contrast with Man 

 in the form and structure of the upper surface of the cranium than the great male 

 Chimpanzee does. 



In the basal comparison of the skulls most of the differences pointed out in my former 

 memoir between the Troglodytes niger and Man are repeated, but are the more striking 

 as being presented on a larger scale by the Troglodytes Gorilla. As a consequence, 

 however, of the enormous development of the lambdoidal crest, which carries further 

 backwards and outwards the flattened occipital region, the foramen magnum appears to 

 be more advanced in position than in the Troglodytes niger ; but this seeming nearer 

 approach to the human structure disappears when the base of the skull is viewed in true 

 perspective, placed upright with the palatal surface perpendicular, as in Plate LXIII. 



The basioccipital (T) is longer, thicker vertically, flatter below, and broader in front 

 than in Man ; it sends out short precondyloid processes or prominences into the jugular 

 foramina (/) on each side ; these are overlapped by the synonymous processes (p j) of 

 the petrosal anterior to the precondyloid holes {p) : the basioccipital does not anchylose 

 with the basisphenoid ; both extend straight forwards, parallel to the plane of the palate, 

 instead of curving from below upwards and forwards as in Man. The fissuru lacera 

 media (/), which divides the basioccipital from the petrosal (le), is longer and narrower, 

 and does not expand at its fore-part : the posterior border of the basioccipital becomes 

 less expanded where it joins the condyles. 



The occipital condyles ( 2') are much smaller compared with the size of the skull than 

 in Man ; they are also less convex and more rounded at their extremities ; they are 

 wider apart, and their axes diverge at a more open angle from before backwards. The 

 posterior condyloid fossa (c/) extends forwards along the outer side of the condyle to 

 the jugular process (j p) ; in Man it usually terminates in a post-condyloid foramen, 

 and is filled up by the rough paroccipital ridge which sometimes developes a small (par- 

 occipital) process ; this is represented by a feeble tuberosity below the jugular process 

 (j p) in the Chimpanzee, in which there are no post-condyloid holes. The sutures 

 between the exoccipitals (2) and mastoids (s) remain, but the rest of the lambdoidal 

 suture is obliterated in the Chimpanzee : the extent of the exoccipitals outside the con- 

 dyles is less than in Man. 



The supraoccipital (3) is a much broader plate than in Man, and is flat or slightly 

 concave externally, with all trace of the superior angle lost in the anchylosis con- 

 sequent on the development of the great lambdoidal ridge : it shows nothing answering 



3 k2 



