THE INTERNAL CAPSULE 33 



nucleus. The fibres of the internal capsule can be traced 

 down from the cortex above into the ventral portion of the 

 cerebral peduncle, and in their course they pass between 

 the lentiform nucleus, on the lateral side, and the caudate 

 nucleus and the thalamus, on the medial side. The arteries 

 which supply the basal ganglia and the internal capsule 

 arise from the middle cerebral (p. 119), as it lies below the 

 anterior perforated substance, and they pass upwards over the 

 lateral aspect of the lentiform nucleus. They bend medially 

 and pierce the nucleus, giving it numerous branches. There- 

 after they traverse the internal capsule and terminate on the 

 caudate nucleus and the thalamus. The artery of cerebral 

 hemorrhage passes through the internal capsule a little behind 

 the genu. 



The motor fibres, which arise in the cortex of the anterior 

 central gyrus, converge as they pass towards the internal 

 capsule. And, at the same time, the fibres connected with 

 the uppermost part of the gyrus incline backwards, while those 

 connected with its lowermost part incline forwards. As a 

 result, the motor fibres for the muscles of the tongue, face 

 and head come to occupy the genu of the internal capsule, 

 and lie in front of the fibres for the upper limb. Behind the 

 fibres for the upper limb lie the motor fibres for the muscles 

 of the trunk, while the fibres for the lower limb extend as 

 far backwards as the middle of the posterior limb of the 

 internal capsule. 



In this part of the brain, therefore, all the motor fibres are 

 crowded together in the genu and the anterior half of the 

 posterior limb of the capsule, and it is probable that many 

 sensory fibres accompany them. It must be remembered that 

 all these fibres cross the median plane, either in the brain- 

 stem or in the spinal medulla, before they reach their ultimate 

 destinations, and that lesions of the internal capsule, therefore, 

 produce their effects on the opposite side of the body. When 

 the " artery of cerebral haemorrhage " ruptures, the extrava- 

 sated blood presses on the fibres in the anterior half of 

 3 



