246 SPECIAL PHYSIOLOGY. 



named the aqueduct of Sylvius, with the third ventricle of the cere- 

 brum, and forming the so called fourth ventricle. 



The Pans Varolii. This part, already frequently mentioned, is 

 composed superficially of transverse commissural white fibres, which 

 connect the two halves of the cerebellum. But its deeper parts con- 

 tain, intermixed, however, with other transverse, circular, or arciform 

 fibres, the numerous longitudinal fibres which are continued from the 

 base of the cerebrum, and from the cerebellum to the medulla oblon- 

 gata. The undermost longitudinal fibres connect the cerebral pedun- 

 cles with the anterior pyramids of the medulla; whilst the fibres towards 

 the back of the pons, partly serve to connect the cerebrum with the 

 posterior and lateral columns of the medulla, and partly join the cere- 

 bellum to the restiform bodies of the latter. In the interior of the 

 pons is found, moreover, a large quantity of diffused gray matter. 



The medulla oblongata. The medulla oblongata, Fig. 59, e, may 

 be regarded as chiefly forming an extension downwards of the pedun- 

 cles of the cerebrum, and of the inferior peduncles of the cerebellum. 

 Like those parts, it consists of two halves, which, however, are only 

 slightly marked off from each other, in the middle line, in front and 

 behind. In front, is seen a slight median longitudinal fissure, which, 

 moreover, is interrupted by numerous obliquely intersecting bands of 

 white nervous substance. On each side of this fissure, are two nar- 

 row columns of white substance, named the anterior pyramids ; outside 

 these, are two oval eminences, named the olivary bodies; external to 

 these, and therefore at the side of the medulla, are, in succession, the 

 lateral columns, the tubercles of Rolando, the restiform bodies, and at 

 the back, on either side of the middle line, the posterior pyramids. 

 At the back of the medulla oblongata, the restiform bodies and the 

 posterior pyramids, are seen to diverge as they are traced upwards; 

 and the latter bound below an angular space, which is the floor of the 

 fourth ventricle. On this floor are seen certain important eminences, 

 two on each side, formed by special accumulations of gray matter, and 

 giving origin to large nerves; certain white transverse streaks, which 

 are the roots of the auditory nerves, are likewise seen; and, lastly, a 

 pointed depression, directed downwards in the middle line, correspond- 

 ing with the tip of the so-called calamus script orius, and leading into 

 a canal in the spinal cord. 



The anterior pyramids of the medulla oblongata, are composed 

 entirely of white fibres, and are continuous upwards through the pons, 

 with the under part of the peduncles of the cerebrum, and downwards 

 with the anterior or lateral portions, or so-called columns, of the spinal 

 cord. Most of the fibres of the anterior pyramids pass obliquely 

 across the median fissure, partly to the anterior, but chiefly to the 

 lateral, columns of the opposite side of the cord, so that the fissure 

 here is interrupted, as already stated, by intersecting bundles of fibres, 

 which form the so-called decussation of the pyramids; some of these are 

 said to pass down into the posterior part of the spinal cord; a certain 

 number of the outermost fibres of the pyramids do not decussate, but 

 descend into the anterior columns of the cord on their own side. The 

 olivary bodies consist, internally, of a folded or plicated sac of gray 



