CHAPTEK XX. 



The Pons and the Cebebellum. 



It was learned in the foregoing chapter that the bundles of fibers from 

 the cerebrum and the thalamencephalon' are, in the region of the mesen- 

 cephalon, arranged in two different layers: the pes peduneuli and the teg- 

 mentum. Posterior to the corpora quadrigemina the aqu£eductus becomes 

 much widened. The pes and the tegmentum pass under it farther down- 

 ward into the metencephalon. Only one constituent of the tegmentum, 

 the anterior peduncle of the cerebellum, which originates in the red nucleus, 



tflTM'fllLtttttl. 



Fig. 200. — The pedunculus cerebri and the pons as seen anteriorly. The 

 tract of pedal fibers, which does not terminate in the pons, is shaded. Hirn- 

 shenkel, Pedunculus cerebri. Klcinhirii, Cerebellum. 



passes now from the floor of the mesencephalon dorsally to the roof of the 

 metencephalon. This roof develops into the cerebellum. That portion of 

 the central canal which lies under it is the continuation, of the aqueduct 

 and is called the fourth ventricle. The floor and lateral portions of the 

 metencephalon contain the continuation of the pes and tegmentum. 



Note first what becomes of the fibers of the pes: Not far posterior to 



' See also Chapters XVI and XVII. 

 (310) 



