62 THE ANATOMY OF VERTEBRATED AKDIALS. 



Sylvian fissure, at In^ there is an elevation wliicli answers to 

 the insula., or central lobe. 



In the Chimpanzee, the olfactory nerves, or rather lobes, 

 are, relatively, very small, and the tracts which connect them 

 with the uncinate gyri {suhstantm perforatiGe) are comjoletely 

 hidden by the temporal gyri ( C^\ The Sylvian fissure is very 

 long and deep, and begins to hide the insula., on which a few 

 fan-shaped gyri are developed. The frontal lobes are very 

 large, and overlap the olfactory nerves for a long distance ; 

 while the occipital lobes completely cover and extend beyond 

 the cerebellum, so as to hide it completely from an eye placed 

 above. The gyri and sulci have now attained an arrangement 

 which is characteristic of all the highest Mainrnalia. The 

 fissure of Rolando {It) divides the antero-parietal gyrus i^A. P) 

 from the postero-parietal (P.P). These two gyri, with the 

 postero-parietal lobule {P.PL), and part of the angular gyrus 

 (A7i)j constitute the I*arietal lobe. The frontal lobe, which 

 lies anterior to this, the occipital lobe, which lies behind it, 

 and the temporal lobe, v/hich lies below it, each present three 

 tiers of gyri, which, in the case of the frontal and occij^ital 

 lobes, are called superior, middle, and inferior — in that of the 

 temporal lobe, anterior, middle, and posterior. The inferior 

 surface of the frontal lobe, which lies on the roof of the orbit 

 (xS. Or?)., presents many small sulci and gyri. 

 ^ On the inner face of the cerebral hemisphere (Fig. 22) the 

 o^ sulcus presented by the Rabbit's brain is that deep and 

 broad depression (jK) which runs parallel with the posterior 

 pillar of the fornix, and gives rise, in the interior of the de- 

 scending cornu of the lateral ventricle, to the projection which 

 is termed the hippocampus major. In the Pig, this hippocam- 

 pal sulcus {PT) is much narrower and less conspicuous ; and a 

 marginal (ilT) and a colossal ( C) gyrus are separated by a 

 well-marked calloso-marginal sulcus. As in the Rabbit, the 

 uncinate gyrus forms the inferior boundary of the hemisphere. 

 In the Chimpanzee, the marginal and callosal gyri are still 

 better marked. There is a deep internal perpendicular, or 

 occipito-parietal., sulcus [P.]^, The calcarine sulcus {Ca) 

 causes a projection into the floor of the posterior cornu, 

 which is the hijyj^ocam pus minor ^ while the collateral sulcus 

 (Coll) gives rise to the eminence of that name in both the 

 posterior and descer^dmg cornua. The hippocampal sulcus 

 {S^ is relatively insignificant, and the lower edge of the tem- 

 poral lobe is formed b}'' the posterior temporal g}Tus. 



In tlie Rabbit, the corpus callosum is relatively small, much 



