The Cerebrum. 425 



nally, and the lenticular nucleus externally. After pass- 

 ing down between these bodies, i.e., between the caudate 

 nucleus and the optic thalamus on the inner side and the 

 lenticular nucleus on the outer side, the projection fibres 

 pass under the optic thalamus to the crus cerebri and thence 

 into the pons, medulla and cord. The portion of the in- 

 ternal capsule between the caudate and the lenticular nu- 

 cleus is shorter than that between the latter and the optic 

 thalamus and the angle at which these two parts join is 

 termed the knee-like bend or genu of the internal capsule. 

 The Relative Position of the Fibres forming the 

 internal capsule, is as follows : In front, between the cau- 

 date and the lenticular nucleus, i.e., in the anterior limb, 

 are the fibres that pass down from the frontal lobe. Some 

 of these fibres terminate in the grey nuclei of the pons, 

 while others pass through the middle peduncle to the cere- 

 bellum and associate the latter with the frontal lobe. The 

 genu or knee and the anterior two-thirds of the posterior 

 limb of the internal capsule contain motor fibres for the op- 

 posite side of the face, tongue and body. Those for the face, 

 i.e., the facial tract, cross the middle line of the pons to 

 end in the nucleus for the facial nerve in the lower part of 

 the pons ; while those for the tongue, i.e., the hypo-glossal 

 tract, terminate in the nuclei for the hypo-glossal nerve in 

 the upper part of the medulla. Both tracts are situated 

 at the genu or knee of the internal capsule, just in front of 

 the motor fibres for the rest of the body. Immediately 

 behind these cranial tracts in the internal capsule, are the 

 motor fibres for the arm, trunk and leg, situated in the 

 order named (Fig. 12). These motor fibres of the pro- 

 jection system pass down, after leaving the internal cap- 

 sule, beneath the optic thalamus ; then in the crus cerebri 

 as a part of the crusta or "foot of the crus" (Fig. 13) ; 

 then through the pons and medulla to decussate (the ma- 



