532 THE CEREBRUM. 



of study by various anatomists in earlier and recent times, but still re- 

 quires farther elucidation. An attempt to describe minutely all the indi- 

 vidual gyri would be difficult and useless, owing to their irregularity in 

 different cases, and their want of symmetry in the same brain. .Nevertheless, 

 there are some sufficiently constant in presence, and characteristic in situa- 

 tion and form, to admit of being specially described ; and it seems probable 

 that, by a sufficiently careful comparison of the convolutions in different 

 animals, and the observation of their development in the foetus, certain 

 general facts may be ascertained regarding them, tending to throw light 

 upon their disposition in man. 



Fig. 364. 



Fig. 364. OUTLINE OP THE CHREBRUM AS SEEN FROM THE LEFT SIDE, SHOWING THE 

 CONVOLUTIONS AS DISTINGUISHED BI GRATIOLET. f 



F, frontal lobe ; P, parietal lobe ; T, temporal lobe ; 0, occipital lobe ; R, R, fissure 

 of Rolando ; s, s. fissure of Sylvius, posterior division : s', s', its anterior division ; C, at 

 the junction of the two, marks the place of the central lobe or convolutions of the island 

 of Reil ; p, the place of the vertical or occipital fissure ; , a', a", superior, middle and 

 inferior frontal convolutions ; a*, supraorbital convolutions ; A, anterior transverse or 

 ascending parietal convolution ; B, posterior transverse or ascending parietal convolution ; 

 &, &', b", upper, middle and lower parietal convolutions ; c, c', c", upper, middle and 

 lower temporal convolutions; d, d', d", upper, middle and lower occipital convolutions ; 

 between b, b', b", and d, d' } d", are seen the connecting convolutions ; between c and c', 

 the parallel fissure. 



The island of Reil constitutes the set of convolutions (gyri operti) which 

 appear earliest both in the fostus and in the animal series, It is a 

 triangular eminence, broken externally into short radiating convolutions, 

 which forms a delta between the anterior and posterior division of the 

 fissure of Sylvius, and is limited externally by a deep sulcus. This mass, 

 constituting the central lobe of recent authors, derives additional interest 

 from being the centre round which the principal convolutions of the cere- 

 brum are arranged. It is only brought into view by laying open the fissure 

 of Sylvius. (See Figs. 368 and 377.) 



The convolution of the Sylvian fissure is a very large convolution, which is 

 also early in its appearance in animals. Commencing in front of the inner 

 end of the Sylvian fissure, it takes a tortuous and much folded course all 

 round that fissure, giving off numerous secondary gyri, and terminates behind 

 the fissure opposite the point where it began. 



The gyrus fornicatus, convolution of the corpus callosum, or internal con- 



