THE CRURA CEREBRL 521 



pally formed of nerve-fibres, of which the inferior or more 

 superficial are continuous with those of the anterior pyra- 

 midal tracts of the medulla oblongata, and the superior or 

 deeper fibres with the lateral and posterior pyramidal tracts, 

 and with the olivary fasciculus. Besides these fibres from 

 the medulla oblongata, are others from the cerebellum; and 

 some of the latter as well as a part of the fibres derived 

 from the lateral tract of the medulla oblongata, decussate 

 across the middle line. 



On their upper part, the crura cerebri bear three pairs 

 of small ganglia, or masses of mingled grey and white 

 nerve-substance, namely, the corpora geniculata externa and 

 internet, and the corpora quadrigemina, or nates and testes. 

 And in their onward course to the cerebrum, the fibres of 

 each crus cerebri pass through two large ganglia, the optic 

 thalamus and corpus striatum, and in their substance come 

 into connection with variously-shaped masses and layers 

 of grey substance. Whether all the fibres of the crura 

 cerebri end in the grey matter of these two ganglia, while 

 others start afresh from them to enter the cerebral hemi- 

 spheres ; or whether some of the fibres of the crura pass 

 through them, while only a portion can be strictly said to 

 have their termination there, must remain at present 

 undecided ; the difficulties in the way of solving such an 

 anatomical doubt being at present quite insuperable. 



Each crus cerebri contains among its fibres a mass of 

 vesicular substance, the locus niger, the nerve- corpuscles of 

 which abound in pigment-granules, and afford some of the 

 best instances of the caudate structure. 



With regard to their functions, the crura cerebri may 

 be regarded as, principally, conducting organs. As nerve- 

 centres they are probably connected with the functions of 



7, 8, 9, 10, the cerebellum; -f , the inferior vermiform process. The 

 figures from I. to IX. are placed against the corresponding cerebral 

 nerves ; III. is placed on the right crus cerebri ; VI. and VII. on the 

 pons Varolii ; X. the first cervical or suboccipital nerve. 



