246 A MANUAL OF ANA TO MY. 



Within the stalk of white matter are situated four pairs 

 of gray nuclei. The most conspicuous pair, situated within 

 the centre of the white matter, is an oval nucleus with a 

 dentated or serrated outline, and in consequence is called 

 the corpus dentatum. 



The Pons. Figs. 29, 38 to 40, 47 to 49, 53. 



This is the portion of brain which intervenes between the 

 crura and the medulla, and consists of anteroposterior 

 fibres crossed transversely by the fibres connecting the 

 hemispheres of the cerebellum as stated above. 



The pons is about an inch wide along the median line 

 and narrows to half that width as it enters the cerebellum. 

 It presents a shallow depression, in the middle line in which 

 the basilar artery rests. See page i 58. 



The upper and lower or anterior and posterior borders 

 of the pons are well marked. At the upper border the 

 crura cerebri pass backward out of sight, and at the lower 

 border their continuation appears as the medulla. 



The posterior surface of the pons will be described with 

 the fourth ventricle, of which it forms the anterior portion. 



On section, the pons presents two distinct areas. The 

 ventral or anterior, and the tegmental or posterior (continu- 

 ous with the tegmentum of the crura cerebri). The de- 

 scription of the subdivisions of these regions belongs to the 

 histology of the brain. 



The cerebellum and the pons are developed from the 

 hindbrain, the former from its roof and the latter from its 

 floor, while the cavity of the hindbrain remains as the an- 

 terior part of the fourth ventricle. 



The Medulla. Figs. 29, 53, 54. 



This portion of the brain extends from the pons back- 

 ward for about an inch and a quarter to the margin of the 



