520 THE NERVOUS SYSTEM. 



On their tipper part the crura cerebri bear three pairs 

 of small ganglia, or masses of mingled grey and white 

 nerve-substance, namely, the corpora yeniculata externa 

 and intern-a, and the corpora quadrigemina, or nates and tastes. 

 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 insuperable. 



Each crus cerebri contains among its fibres a mass of 

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

 which abound in pigment-granules, and aiford 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 

 the third cerebral nerve, which arises from the locus niger, 

 and through which are directed the chief of the numerous 

 and complicated movements of the eyeball and iris. 



From the result of vivisection it appears that when one 

 of the crura cerebri is cut across, the animal moves round 

 and round, rotating around a vertical axis from the injured 

 towards the sound side. Such movements, however, attend 

 the sections of other parts than the crura cerebri : 

 and as indications of the functions of these parts, the 

 results of such experiments have been hitherto almost 

 valueless. 



Corpora Quadrigemina. The corpora quadrigemina (from 



