136 Mammalia. 



of the Quadrilateral Lobule, to the summit of the Occipital Lobule, 

 where it is continuous with the Superior External Bridging Convo- 

 lution: and, the Inferior Internal Bridging Convolution which unites 

 the base of the Quadrilateral Lobule with the Inferior extremity of 

 the Occipital Lobule. 



If the Brain of Man be taken as the standard of Cerebral develop- 

 ment, the position of any Ape in a classification, which has the 

 Kervous system for its basis, will depend upon the degree in which 

 its brain resembles that of Man. 



The most striking features of the Human Brain are 



1 . Its great size and complexly convoluted surface. 



2. The great development of the Frontal Lobe ; and especially of 

 the Superior Frontal Convolution, which is indicated, 



{a.) By the position of the upper extremity of the Fissure of 

 Rolando, which reaches the superior border of the Hemisphere at a 

 point much further back than in the Apes' Brains : 



(5.) By the Antero-Parietal Sulcus meeting the Fissure of Sylvius, 

 not just above the Bend of the Fissure of Sylvius, as in most Apes, 

 but considerably further back : 



{c. ) By the horizontal position of the Fissure of Sylvius, which is 

 more especially due to the great development of the Superior 

 Frontal Convolution. 



3. The small extent of the Occipital Lobe. 



4. The comparatively small, and but slightly projecting Tcmporo- 

 sphenoidal Lobe. 



5. The Obliteration of the External Perpendicular Fissure, owing 

 to the great size of the two Superior External Bridging Convolutions, 

 both of which are superficial. 



6. The great Antero-posterior extent of the Corpus Callosum. 



Amongst the Old "World Apes there are three groups, headed 

 respectively by the Orang-Ftang (Simla Satyrus), the Chimpanzee 

 (Simla Troglodytes), and the Gorilla, in each of which Cerebral 

 development seems to be progressing on a different plan. 



Thus, in the group of which the Orang is chief, in which the brain 

 appears to be developing in the same direction as that of Man, the 

 Frontal and Parietal Lobes gradually increase in size and complexity, 

 the Occipital d^x^iim.'&iim^ pari passu: in the Chimpanzee the Frontal 

 and Occipital lobes are most developed: whilst in the Gorilla the 

 Parietal and Occipital Lobes predominate. 



