788 THE CENTRAL AXIS OF THE NERVOUS SYSTEM. 



the posterior part of the inferior face of the hemisphere (Figs. 423, 18, 19 ; 433, 

 18, 19). It is curved on itself, the convexity being outwards, and its inner 

 border is related to the crus cerebri. It concurs in forming the great longi- 

 tudinal fissure, its large extremity being turned forwards and margins the fissure 

 of Sylvius, while the posterior extremity disappears in the posterior lobe of the 

 hemisphere. 



The surface of the temporal lobe is almost smooth, and shows scarcely more 

 than one slight fissure, parallel to the posterior branches of the fissure of Sylvius 

 (Fig. 433). This fissure (the parallel fissure) terminates more or less directly 

 behind, between the branches of a ^ convolution — the curved j^lffit- The 

 external branch of the latter is continuous with the superior temporal convolution 

 (Fig. 433, 19), which is comprised between the parallel fissure and the fissure of 

 Sylvius. The part situated below the parallel fissure (Fig. 433, 18) represents 

 the second and third temporal convolutions of Man. The temporal lobe is very 

 simple in Solipeds, and is hollowed internally by a cul-de-sac cavity that consti- 

 tutes the bottom of the posterior or reflected portion of the lateral ventricles. 



d. Lobule of the curved plait. — Nearly quadrilateral in shape (Figs. 423, 13 ; 

 433, 10), this lobule is included between the fissure of Sylvius, the inferior part 

 of the fissure of Rolando, and the interparietal fissure. It is formed by a large 

 convolution, confounded at its commencement with the ascending frontal convo- 

 lution, and which soon divides into two undulating plaits that unite, behind, 

 with the superior temporal convolution, the curved plait, and sometimes with 

 the convolutions of the parieto-occipital lobe. 



e. Parieto-occipital lobe. — The limits of the occipital lobe — so difficult to 

 establish in the human brain — cannot be determined in that of the Horse ; for 

 this reason it is that we now describe a parieto-occipital lobe resulting from the 

 fusion of the parietal with the occipital lobe. 



This lobe offers three faces. The external face is almost entirely occupied 

 by a large convolution — the parieto-temporal — formed by two folds, the outer of 

 which (Figs. 323, 7, 7 ; 433, 12, 12) margins the interparietal fissure and the 

 anterior part of the fissure of Rolando ; in front, it is continuous with the plait 

 that surrounds the crucial fissure and — through the medium of the latter — the 

 first frontal convolution ; behind, it is inflected downwards to be continued on 

 the posterior face of the lobe. 



The internal face shows the parieto-occipital portion of the corpus callosum 

 convolution, and of the second parieto-occipital convolution ; these two being 

 separated by the calloso-marginal fissure, from which is detached a branch that 

 rides on the superior border of the hemisphere and forms the crucial fissure. 



The second parieto-occipital convolution (Figs. 423, 8, 8 ; 433, 13) has the 

 form of a wedge, the summit of which is directed forward ; here it is single, 

 and is confounded with the first convolution of the same lobe, and with the 

 plait that surrounds the crucial fissure ; but it afterwards divides into two 

 principal, almost straight plaits, which are continued on the posterior face of the 

 lobe. 



The latter is occupied by the posterior extremity of the parieto-occipital 

 convolutions. It is oblique downwards and forwards, and is separated from the 

 cerebellum by the transverse duplicature of the dura mater. On this face are 

 seen three or four undulating plaits which join each other, and pass on to the 

 convolutions of the hippocampus. 



