364 SPECIAL ANATOMY. 



b. Corpora olivaria, much shorter than the last (six lines long), 

 on the outer side of which they are placed, directed downwards 

 and inwards. Above they are separated from pans Varolii by a 

 deep fossa, below they are bounded by arched fibres, internally by 

 the roots of N. hypoglossus, and they reach as far as the central 

 line. On their outer border, fasciculi of fibres ascend from the 

 spinal cord (funiculus siliquce externus), and pass through pons 

 Varolii to the sides of corpp. quadrigemina (crura ad corp. qua- 

 drig.}, and form the superior roof of the aquceductus Sylvii. 



The posterior surface of the medulla oblongata is covered by the 

 cerebellum, and presents above a V-shaped fissure, calamus scrip- 

 torius, which forms the anterior wall of the fourth ventricle ; 

 externally the 



c. Corpora restiformia s. crura cerebelli inferiora, the posterior 

 pyramids, the superior extremity of which is enlarged in the form 

 of a nipple, and are, in a manner, the roots of the cerebellum, con- 

 sist of tortuous fibres. 



2. Pons Varolii s. protuberantia annularis, white, cubical, 

 placed above med. oblong, from the centre of clivus to the proc. 

 clinoid. posit., in a depression before the small brain, below the 

 corpp. quadrigem. and the cerebrum. In the middle of the inferior 

 surface, directed obliquely upwards and forwards, it presents a 

 longitudinal sulcus (for 'art. basilaris), on the sides of which the 

 prolongations of the corpp. pyramidalia proceed ; farther, trans- 

 verse fibres, from which the crura cerebelli pass off; and from be- 

 tween which N. trigeminus arises. From the anterior border, the 

 crura cerebri pass forth ; from the lateral, the crura cerebelli; at 

 the posterior, the pyramids enter. The superior surface forms the 

 floor of the fourth ventricle. 



3. Crura cerebri, two thick, cylindrical, white cords, six lines 

 long, diverging from the anterior border of the pons, forwards, up- 

 wards and outwards to the great brain, where they become broader 

 and flatter, and are embraced by tractus nerv. opticorum. Below 

 and at the sides free, they unite above with the corpp. quadrige- 

 mina and crura cerebelli superiora. They form the continuations 

 of the pyramids. Between them is a triangular space which is 

 filled up by the three following parts : 



4. Substantia perforata media, basis ventriculi 3 ; this gray 

 perforated plate consists of two triangular fasciculi (separated 

 from the crura cerebri by a black line), and forms the poste- 

 rior part of the floor of the third ventricle. Here arises N. 

 oculomotorius. 



5. Corpora mamillaria s. bulbi fornicis, two half globules, the 



