SURFACES. 



147 



the quadrigeminal lamina, which forms the greater part of the 

 posterior surface of the mid-brain (Fig. 44). This lamina rests 

 upon the dorsum of the pedunculi cerebri. The pedunculi cerebri 

 are made up of three great di visions, as shown above; named from 

 before backward, they are: (i) The bases pedunculi, comprising 

 the [anterior part; (2) the substantia nigra, which is the middle 

 part; and (3) the tegmenta, which are united by a median raphe 



h i 



Fig. 43. The region of the mid-brain showing pulvinar of the thalamus, the gen- 

 iculate bodies, the corpora quadrigemina and brachia, the pineal body, the 

 optic tract and the fourth nerve. (Original.) 



a. Chorioid groove, b. Medial geniculate body. c. Lateral geniculate body. d. Medial 

 and lateral roots of optic tract, e. Optic tract, f . Optic chiasma. g. Brachium inferius. 

 h. Superior colliculus of corpora quad. i. Pineal body. j. Inferior colliculus of corpora 

 quad. k. Brach. superius. 1. Thalamus. m. Fraenulumveli. n. Superior medullary velum. 

 o. Fourth ventricle, p. Trochlear nerve. 



and lie in the posterior region next the quadrigeminal lamina. 

 In the median plane between the quadrigeminal lamina and the 

 'tegmenta runs the cerebral aqueduct. 



The bases pedunculi (Figs. 45, 46, 47 and 48) are two rounded 

 bands of medullated fibers, limited by the interpeduncular fossa 

 and lateral sulcus of the mid-brain. Each basis pedunculi is a 

 half-inch broad and is distinctly striated longitudinally. It 



