774 DISSECTION OF THfi 



which are contained respectively in the crusta and the tegmeiituni. 



their origin. In this region they are reinforced by the superior peduncles of the 

 cerebellum, and by fibres derived from the corpora quadrigemina, 

 as well as by others springing from the grey nuclei of the crura. 



Fibres of The fibres of the crusta enter the internal capsule ; and while some 

 (including the pyramidal tract) are continued without interruption 

 through this into the medullary centre of the hemisphere, others 

 pass into the lenticular and caudate nuclei, and fresh fibres are 



and of added from those bodies. The longitudinal fibres of the tegrnentum 

 um ' end for the most part in the grey matter of the optic thalamus, 

 from the outer side of which also numerous fibres are given off to 

 the capsule ; but one tract of tegmental fibres, prolonged from the 

 fillet, passes beneath the thalamus into the hinder part of the 

 internal capsule, some of the outer fibres inclining to the side and 

 traversing the inner part of the lenticular nucleus as they course 

 upwards. 



Dissection Dissection. A complete systematic view of the ascending fibres 

 f them cannot now be obtained on the imperfect brain. At this stage the 

 chief purpose is to show the passage of the radiating fibres from 

 the cms through the large cerebral ganglia. 



in the corpus To trace the ascending fibres through the corpus striatum, the 

 um ' caudate nucleus of this body should be scraped away (fig. 282); 

 and the dissection should be made on the lelt side, on which the 

 striate body and the optic thalamus remain uncut. In this pro- 

 ceeding the internal capsule comes into view, consisting of white 

 fibres with intervening grey matter of the corpus striatum, giving 

 the appearance of the teeth of a comb (pecten of Reil). 



On taking away completely the hinder part of the caudate 

 nucleus, others of the same set of fibres will be seen issuing from 

 the outer side of the optic thalamus, and radiating to the posterior 

 and inferior portions of the hemisphere. 



Ascending Arrangement of the ascending fibres. The fibres of the internal 



out*in hprea( capsule diverge as they pass through the grey matter of the corpus 



hemisphere, striatum, and at the outer margin of that body they enter the 

 medullary centre of the hemisphere, where they decussate with the 

 transverse fibres of the corpus callosum, and radiate to all parts of 

 the hemisphere. The ascending fibres thus form in the hemisphere 



forming a part of a hollow cone, named the corona radiata, the apex of 



radiate which is towards the crus cerebri, and the concavity turned down- 

 wards. The base of the cone is at the surface of the hemisphere, 

 where the fibres pass into the grey cortex of the convolutions. 

 From the foregoing description it will be evident that the fibres 

 constituting the corona radiata are of two kinds, viz., those extend- 

 ing without interruption from the cortex to the crus cerebri, and 

 those uniting the cortex with the corpus striatum and optic thalamus. 



Transverse The transverse or commissural fibres connect the hemispheres of 

 the cerebrum across the median plane. They give rise to the great 

 commissure of the corpus callosum, and to the anterior commissure. 

 These bodies have already been examined. 



Longitu- Longitudinal or collateral fibres. These are connecting fibres 



dinal fibres, ' 



