22 ON THE AFFINITIES OF THE BRAIN 



M. Gratiolet in his invaluable ' Memoire sur les Plis Cerebraux de 

 l'Homme et des Primates,' so often referred to. 



Fig. i is a lateral view of the brain of the orang. It shows the following points : — 



i. The even curve described by the superior boundary line of the hemispheres. 



ii. The vertical direction of the fissure of Sylvius, F. 



iii. The failure of the posterior lobes to cover the cerebellum entirely. 



iv. The diminished downward growth of the posterior lobes, as shown by the 

 obliquity of a line drawn along their surface where it lies upon the cerebellum, C. 



v. The presence of the outer part of the lateral vertical fissure, which outer part 

 is always filled up in man, even when the inner may not be so, as the inner is in 

 the orang. 



Fig. 2 is a basal view of the same brain. It shows the following points : — 



i. The great relative thickness of the nerves to the mass of the brain. (See 

 Gratiolet, 'Bull. Soc. Anth.' iv. 1861, p. 252.) 



ii. The absence of any marked excavation of the orbital lobes. 



iii. The lateral and posterior development of the cerebellar hemispheres. 

 Fig. 3 represents the brain of the orang as seen from above. It shows the following 

 points : — 



i. The greater extent to which the cerebellum has come into view on the left side 

 than on the right. 



ii. The want of symmetry between the two sides of the cerebellum. The longi- 

 tudinal fissure seems on the left to be bounded by a continuous vertically unindented 

 table-land, on the right by a table-land indented at two points. The posterior of these 

 two points corresponds to the external vertical fissure, the first or superior pli de 

 passage a a being partially concealed under the operculum, and allowing us thus to 

 mark off the occipital from the principal lobes nearly as sharply as in the chimpanzee. 

 The three frontal convolutions, 1, 2, 3, the two ascending parietals, 4, 5, and the 

 lobule of the second ascending convolution, 5', are asymmetrical on the two sides of 

 the brain. 



iii. The absence of the second pli de passage is well seen on both sides of the 

 brain ; and the wave-like anterior edge of the occipital lobes constituting the ' oper- 

 culum ' is especially well marked on the right side. 



Fig. 4. Brain of orang dissected, so as to show the lateral ventricle of the right side, 

 its three cornua, and the hippocampus minor, 19. It shows, besides, the different 

 relations which the bourrelet of the corpus callosum holds in the ape and in man : — 



i. To the commencement of the third cornu, 18. 



ii. To the internal perpendicular fissure, 16. 



iii. To the hemispheres which it connects. 



1. Inferior frontal convolution. — ' Fjtage frontal infe'rieur' of Gratiolet. 



2. Middle frontal. — ' ^tage frontal moyen.' 



3. Superior frontal. — ' Fjtage frontal superieur.' 



4. First ascending parietal. — ' Deuxieme pli ascendant.' 



5. Lobule of second ascending parietal. — ' Lobule du deuxieme pli ascendant.' 



6 and 6'. Convolution running below, and parallel with the lower lip of the 



Sylvian fissure. — ' Pli courbe.' 

 7. Lower lip of Sylvian fissure. — ' Pli marginal inf^rieur.' 



10. Superior occipital convolution. — ' Fjtage supe'rieur du lobe occipital.' 



11. Middle occipital convolution. — 'Fjtage moyen.' 



12. Inferior occipital convolution. — '£tage infe'rieur.' 



13. Corpus striatum. 



