536 THE CEREBRUM. 



he distinguishes a superior, middle, and inferior tier of convolutions. In the parietal 

 lobe are the anterior and posterior ascending convolutions (convolution of Rolando) 

 surrounding the fissure of Rolando, and behind these a curved lobe. In the temporo- 

 sphenoidal lobe are described a superior, middle, and inferior convolutions, lying 

 parallel to the fissure of Sylvius. The occipital lobe presents also three tiers, but less 

 distinct than those of the frontal, and besides these are four convolutions uniting the 

 occipital and parietal lobes, named by Gratiolet plis de passage, or the connecting 

 convolutions. 



The internal surface^ of the hemisphere Gratiolet divides into the fronto-parietal 

 lobe, corresponding in extent to the frontal and parietal lobes of the external surface, 

 and limited behind by the internal perpendicular fissure, the occipital lobe between 

 that fissure and the fissure of the hippocampi; and the occipito-temporal lobe, 

 including the tentorial surface, and extending outwards to the sphenoido-temporal 

 lobe. 



It is to be remarked, however, that the divisions and nomenclature of Gratiolet, 

 however useful they may be for the purpose of explicit comparison of the convolu- 

 tions of the human brain with those of the quadrumana, the study in which the 

 inventor has made use of them, are yet of a somewhat artificial description, and may 

 not be applicable to a more extended comparison of the disposition of the convolu- 

 tions among animals. 



From Reichert's plates it is apparent that the internal perpendicular fissure (occi- 

 pito-parietal of Huxley) is the upper of two branches into which the fissure of the 

 hippocampi divides posteriorly in its first development, and which together with 

 that fissure constitutes his fissura occipitalis. The inferior branch, the posterior 

 part of the fissure of the hippocampi, is the calcarine fissure of Huxley. 



Not only the comparison of the brain of man with those of other animals, but like- 

 wise the comparison of human brains one with another, establishes the existence of a 

 relation between mental development and the complication, size, and depth of the 

 cerebral convolutions, and the extent of the grey matter contained in them. 



On the subject of the cerebral convolutions the reader may consult, in addition to 

 the works of Arnold, Tiedemann, Foville and Reichert, that of Leuret and Gratiolet 

 "Anat. Comp. du Systeme Nerveux, 1839-57;" Gratiolet, "Mem. sur les Plis 

 C6re"braux de 1'Homme et des Primates, 1854 ; " R. Wagner, " Tiber die typischen 

 Verschiedenh. der Windungen der Hemispharen," &c., Getting. 1860-62 ; Huschke, 

 " Schadel, Hirn und Seele," 1854 ; Huxley, " Brain of Ateles paniscus," Proc. of 

 Zool. Soc., June, 1861 ; J. Marshall, (( On the Brain of a Bush-woman, and on the 

 Brains of Two Idiots, &c.," Trans. Roy. Soc. 1863. 



BASE or THE CEREBRUM. When the brain is turned with its base upper- 

 most, and the parts of which it is composed are allowed to fall slightly 

 asunder by their own weight, two considerable masses, consisting of white 

 substance externally, are seen emerging together from the fore part of the 

 poiis Yarolii, and, separating from each other as they proceed forwards and 

 outwards, to enter the inner and under part of the right and left cerebral 

 hemispheres. These white masses, which are marked on the surface with 

 longitudinal striae, and have somewhat the appearance of large bundles of 

 fibres, are the peduncles or crura of the cerebrum. Immediately before 

 entering the corresponding hemisphere, each is crossed by a flattened white 

 cord, named the optic tract, which, adhering by its upper border to the 

 peduncle, is directed forwards and inwards, and meets in front with its 

 fellow of the opposite side to form the optic commissure, from the fore part 

 of which the optic nerves proceed. 



Limited behind by these diverging peduncles, and in front by the con- 

 verging optic tracts, is a lozenge-shaped interval, called the interpeduncular 

 space, in which are found, in series from behind forwards, the posterior per- 

 forated space, the corpora albicantia, and the tuber cinereum, from which 

 is prolonged the infundibulum attached to the pituitary body. 



The posterior perforated space (locus perforatus posterior) is a deep fossa 



