656 



STRUCTURE OF THE CEREBRUM 



[OIL XLVI. 



symptom. If the motor-fibres are affected, degeneration will occur 

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

 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. 477 represents a horizontal view through the hemisphere. 

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



FIG. 477. 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 ; AF., 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 cms is lettered on the left side. S.N., substantia nigra ; PY M 

 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 

 sensory-fibres, pass. The connection between cerebrum and the 

 cerebellum is also indicated; one cerebral hemisphere is connected 

 with the opposite cerebellar hemisphere by fronto-cerebellar and 

 temporo-occipito-cerebellar fibres which pass respectively in front 

 of and behind the pyramidal fibres in the internal capsule. 



Histological Structure of the Cerebral Cortex. 



The grey matter of the cortex is composed of a number of layers 

 which are, however, not well marked off from one another. The 

 number of these layers is variously given by different authorities 



