242 A MANUAL OF ANATOMY. 



The crura cerebri, quadrigeminal lamina and bodies, and 

 lower arm of the optic tract are developed from the primi- 

 tive midbrain, and the aqueduct of Sylvius is the remains 

 of the cavity within this vesicle. 



The Cerebellum. Figs. 29, 34, 37 to 40, 52 to 56. 



This consists of two symmetrical halves united at their 

 opposing surfaces along a posterior median plane, and 

 also, like the cerebral hemispheres, by a wide cross-band 

 of commissural fibres which passes anterior to the back- 

 ward prolongation of the crura cerebri, and is called the 

 pons. 



The Lobes of the Cerebellum. " In descriptive an- 

 atomy an astounding variety of names are applied to the 

 various parts of each lobe ; it would be an essential gain if 

 at least three-fourths of these names could be discarded." 

 (Minot's " Embryology.") The cerebellum is divided into 

 five primary lobes by four sulci. 



The superior surface of the cerebellum is divided into 

 two lobes, the quadrate and the posterosuperior. The 

 former is subdivided into the anterior and posterior crescen- 

 tic portions. 



The under surface of the cerebellum presents the floccu- 

 lus, a small but prominent rounded lobe close to the pos- 

 terior part of the pons. Behind this and close to the 

 medulla, the tonsillar or amygdaloid lobe. Behind these 

 are the cuneate, slender, and postero-inferior lobes. 



Between the under surfaces of the cerebellar hemispheres 

 is a deep notch the vallecula for the reception of the 

 medulla. 



The junction of the cerebellar lobes along the median 

 plane is marked by a rounded elevation called the superior 

 and the inferior vermis. These are further subdivided by 



