518 THE NERVOUS SYSTEM. 



In the medulla oblongata appears to be seated also tlie 

 chief re/so -motor nerve-centre (p. 5/6). From this arise 

 fibres which, passing down the spinal cord, issue with the 

 anterior roots of the spinal nerves, and enter the ganglia 

 and branches of the sympathetic, by which they are 

 conducted to the blood-vessels. 



The influence which is exercised by the medulla ob- 

 longata, or, at least, by its irritation, on the formation of 

 sugar in the liver, has been referred to (p. 3 36). 



STRUCTURE AND PHYSIOLOGY OF THE PONS YAROLTI, 

 CRURA CEREBRI, CORPORA QUADRIGEMINA, CORPORA 

 GENICULATA, OPTIC THALAMI, AND CORPORA STRIATA. 



Pons Varolii. The meso-cephalon, or pons (vi, fig. 145 ) f 

 is composed principally of transverse fibres connecting the 

 two hemispheres of the cerebellum, and forming its prin. 

 cipal commissure. But it includes, interlacing with these, 

 numerous longitudinal fibres which connect the medulla 

 oblongata with the cerebrum, and transverse fibres which 

 connect it with the cerebellum. Among the fasciculi of 

 nerve -fibres by which these several parts are connected, 

 the pons also contains abundant grey or vesicular sub- 

 stance, which appears irregularly placed among the fibres, 

 and fills up all the interstices. 



The anatomical distribution of the fibres, both trans- 

 verse and longitudinal, of which the pons is composed, is- 

 sufficient evidence of its functions as a conductor of im- 

 pressions from one part of the cerebro- spinal axis to 

 another. 



Concerning its functions as a nerve-centre, little or 

 nothing is certainly known. 



Crura Cerebri. The crura cerebri (in, fig. 145), are prin- 

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

 superficial are continuous with those of the anterior pyra- 



