690 



STRUCTURE OF THE CEREBRUM 



[CH. XLVIII. 



in the pyramidal tract, and can be traced through the pes of the crus 

 and mid-brain to the pyramid of the pons and bulb, and then in the 

 crossed pyramidal tract of the opposite side and in the direct pyra- 

 midal tract of the same side of the cord. 



Fig. 426 represents a horizontal view through the hemisphere. 

 The internal capsule (c) at the point * makes a bend called the genu 



FIG. 426 Diagram to show the connection of the Frontal and Occipital Lobes with the Cerebellum, etc. 

 The dotted lines passing in the crusta (T.OC.), outside the motor fibres, indicate the connection 

 between the temporo-occipital lobe and the cerebellum. F.C., The fronto-cerebellar fibres, which 

 pass anteriorly to the motor tract in the crusta ; I.F., fibres from the caudate nucleus to the pons. 

 Fr. , frontal lobe ; Oc., occipital lobe; A. F., ascending frontal; AP., ascending parietal convolutions ; 

 PCF., precentral fissure in front of the ascending frontal convolution ; FR, fissure of Rolando; IFF., 

 intraparietal fissure. A section of the crus is lettered on the left side. S.N., Substantia nigra ; PV., 

 pyramidal motor fibres, which on the right are shown as continuous lines converging to pass through 

 the posterior limb of i.e., internal capsule (the knee or elbow of which is shown thus *) upwards into 

 the hemisphere and downwards through the pons to cross at the medulla in the pyramidal decussa- 

 tion. Ipt, Crossed pyramidal tract ; apt, direct pyramidal tract. (Gowers.) 



or knee, behind which the motor-fibres, and more posteriorly still 

 the sensory-fibres, pass. Some of the connections between cerebrum 

 and the cerebellum are also indicated. 



The Convolutions of the Cerebrum. 



The surface of the brain is 'marked by a great number of depres- 

 sions which are called fissures or sulci, and it is this folding of the 

 surface that enables a very large amount of the precious material 

 called the grey matter of the cortex to be packed within the narrow 

 compass of the cranium. In the lowest vertebrates the surface of 

 the brain is smooth, but going higher in the animal scale the fissures 

 make their appearance, reaching their greatest degree of complexity 

 in the higher apes and in man. 



