THE BRAIN. 



149 



The division of the cerebellum into a median and two lateral 

 portions, already indicated in Reptiles, but much more plainly 

 marked in Birds, is carried to a still further extent in Mammals. 



FIG. 124. CONVOLUTIONS OF THE HUMAN BRAIN. (After A. Ecker.) 



Lf, frontal lobe ; Lp, parietal lobe ; Lo, occipital lobe ; T, temporal lobe ; a, b, c, 

 superior, middle, and inferior frontal gyri ; X, j8, anterior and posterior 

 central convolutions, separated from one another by the fissTire of Rolando (B) ; 

 em, the calloso-marginal sulcus, on the dorsal surface ; P, P l , superior and 

 inferior parietal gyri, separated from one another by the interparietal fissure 

 (/) ; Po, parieto-occipital fissure ; FS, Sylvian fissure ; 1 to 3, superior, middle, 

 and inferior temporal convolutions ; HH, cerebellum ; NH, medulla oblongata ; 

 R, spinal cord. 



The median portion gives rise to the so-called superior vermis, 

 while the lateral parts form the lateral lobes and flocculi. 



jnr 



FIG. 125. DIAGRAMMATIC FIGURE OF THE PRINCIPAL BANDS OF NERVE-FIBRES 

 OF THE MAMMALIAN BRAIN. (From a drawing by A. Ecker.) 



Cacb, crura medullee ad cerebellum ; Cap, crura cerebelli ad pontem ; Cac, crara 

 cerebelli ad corpora bigemina ; C.C., crura cerebri ; HM, hemispheres ; Cs, corpus 

 striatum ; Th, optic thalamus ; L, lemniscus ; P, pons Yarolii ; HH, cere- 

 bellum. 



The two lateral lobes are connected by a large commissure, the 

 pons Varolii (Fig. 123, P} : this extends round the medulla 

 oblongata ventrally, and is more largely developed the higher we 

 pass in the Mammalian series. 



