BASAL GANGLIA 



577 



Crura Cerebri. The crura are short, thick, rounded bands which 

 pass from the cerebral hemispheres to the upper border of the pons 

 Varolii. They are rather broader above than below and are about three- 

 quarters of an inch (19 millimeters) in length. They are composed of 

 longitudinal white fibres connecting various parts with the cerebrum. 

 Each crus is divided into a superficial and a deep band, by a layer of 

 gray substance called the locus niger. The locus niger contains small 

 multipolar nerve-cells and abundant pigmentary granules. The lower, 

 or superficial band of the crus is called the crusta. The deep band is 



Fig. 142'. Vertical section of the brain, reduced about one-quarter (Dalton). 



I, I, I, I, first frontal convolution ; II, II, second frontal convolution ; III, III, third frontal convo- 

 lution ; CC, corpus callosum ; CS, corpus striatum ; 1C, internal capsule ; LN, lenticular nucleus ; 

 In, insula ; S, fissure of Sylvius. 



called the tegmentum. The crusta consists of white fibres only. In 

 the tegmentum the fibres are mixed with masses of gray matter. 



Pons Varolii. The pons Varolii, called the tuber annulare, cr the 

 mesocephalon, is situated at the base of the brain just above the bulb. 

 It is white externally and contains in its interior a large admixture of 

 gray matter. It presents both transverse and longitudinal white fibres. 

 Its transverse fibres connect the two halves of the cerebellum. Its 

 longitudinal fibres are connected below with the anterior pyramidal 

 bodies and the olivary bodies of the bulb, the lateral columns of the 

 cord and a certain portion of the posterior columns. The fibres are con- 

 nected above with the crura cerebri and pass to the brain. 



