CH. XLV1II.] STRUCTURE OF THE CEREBRUM 689 



end of the nucleus caudatus (n.c.) ; the section being taken somewhat 

 posteriorly. The nucleus lenticularis is marked nl. ; and the band of 

 white fibres passing up between it and the thalamus is called the 

 internal capsule (c.i.)\ the narrow piece of white matter between 

 the claustrum and the lenticular nucleus is called the external 

 capsule (c.e.). 



For the student of medicine the internal capsule is one of the 

 most important parts of the brain. In it are the continuations of 

 the fibres which we have previously traced as far as the crus cerebri ; 

 the motor-fibres of the crusta are continued into the anterior two- 

 thirds of its posterior limb (i.e. behind the genu * in fig. 426) ; the 

 sensory fibres of the tegmentum into the posterior third of this limb. 

 When these fibres get beyond the narrow pass between the basal 

 ganglia, they spread out in a fan-like manner and are distributed to 

 the grey cortex ; the motor-fibres come down from the motor area in 

 front of the fissure of Eolando ; the sensory fibres go to certain con- 

 volutions behind this fissure. The name corona radiata is applied 

 to the fan-like spreading of the fibres; the fibres as they pass 

 through the handle of the fan, or internal capsule, communicate 

 with the nerve-cells of the grey matter of the basal ganglia; the 

 pyramidal fibres on their way down to the medulla and cord from 

 the motor area of the brain send off collaterals or side branches 

 which arborise around the cells of the corpus striatum, and to a 

 less degree around those of the optic thalamus; the axis-cylinder 

 processes of these cells pass out to join the pyramidal tract on its 

 downward course. The sensory fibres on their way up terminate 

 by arborising round the cells of the optic thalamus, and in the 

 subthalamic area. This, in fact, is another cell-station or position of 

 relay : the fibres passing out from the cells of the thalamus continue 

 the impulse up to the cortex. 



The importance of the internal capsule is rendered evident when 

 one considers the blood supply of these parts ; at the anterior and 

 posterior perforated spots, numerous small blood-vessels enter for the 

 supply of the basal ganglia, and these are liable to become diseased, 

 and if they rupture, a condition called apoplexy is the result ; if the 

 haemorrhage is excessive, death may occur almost immediately ; but 

 if the patient recovers, a condition of more or less permanent paralysis 

 remains behind ; and a very large amount of paralysis results from a 

 comparatively limited lesion, because so many fibres are congregated 

 together in this narrow isthmus of white matter. If the haemorrhage 

 is in the anterior part of the posterior limb, motor paralysis of the 

 opposite side of the body (hemiplegia) will be the most marked 

 symptom. If the haemorrhage occurs in the posterior part, sensory 

 paralysis of the opposite side of the body will be the most marked 

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



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