514 NERYOUS SYSTEM. 



divergence of the restiform bodies, and posterior pyramids, becoming blended with 

 the ascending fibres of the lateral column, and thus forming the fasciculi teretes. 

 The lateral crescentic portions, but especially the posterior horns, become enlarged, 

 blend with the fibres of the restiform bodies, and form the tuberculo cinereo of 

 Rolando. 



Special deposits of gray matter are found both in the anterior and posterior 

 parts of the medulla; in the former situation, forming the corpus dentatum 

 within the olivary body, and, in the latter, a series of special masses, or nuclei, 

 connected with the roots of origin of the spinal accessory, vagus, glosso-pharyn* 

 geal, and hypoglossal nerves. It thus appears that the closest analogy in 

 structure, and also probably in general endowments, exists between the medulla 

 oblongata and the spinal cord. The larger size and peculiar form of the medulla 

 depending on the enlargement, divergence, and decussation of the various 

 columns ; and also from the addition of special deposits of gray matter in the 

 olivary bodies and other parts, evidently in adaptation to the more extended range 

 of function which this part of the cerebro-spinal axis possesses. 



PONS VAROLII. 



The pons Varolii (mesocepliale, Chaussier) is the bond of union of the various 

 segments of the encephalon, connecting the cerebrum above, the medulla oblongata 

 below, and the cerebellum behind. It is situated above the medulla oblongata, 

 below the crura cerebri, and between the hemispheres of the cerebellum. 



Its under surface presents a broad transverse band of white fibres, which arches 

 like a bridge across the upper part of the medulla, extending between the two 

 hemispheres of the cerebellum. This surface projects considerably beyond the 

 level of these parts, is of a quadrangular form, rests upon the basilar groove of 

 the occipital bone, and is limited before and behind by very prominent margins. 

 It presents along the middle line a longitudinal groove, wider in front than behind, 

 which lodges the basilar artery ; numerous transverse striae are also observed on 

 each side, which indicate the course of its superficial fibres. 



Its upper surface forms part of the floor of the fourth ventricle, and at each side 

 it becomes contracted into a thick rounded cord, the crus cerebelli, which enters 

 the substance of the cerebellum, constituting its middle peduncle. 



Structure. The pons Yarolii consists of alternate layers of transverse and longi- 

 tudinal fibres intermixed with gray matter (fig. 263). 



The transverse fibres connect together the two lateral hemispheres of the 

 cerebellum, and constitute its great transverse commissure. They consist of a 

 superficial and a deep layer. The superficial layer passes uninterruptedly across 

 the surface of the pons, forming a uniform layer, consisting of fibres derived from 

 the crus cerebelli on each side, which meet in the median line. The deep layer 

 of transverse fibres decussates with the longitudinal fibres continued up from the 

 medulla, and contains much gray matter between its fibres. 



The longitudinal fibres are continued up through the pons. 1. From the 

 anterior pyramidal body. 2. From the olivary body. 3. From the lateral and 

 posterior columns of the cord, receiving special fibres from the gray matter of the 

 pons itself. 



1. The fibres from the anterior pyramid ascend through the pons, imbedded 

 between two layers of transverse fibres, being subdivided in their course into 

 smaller bundles ; at the upper border of the pons they enter the crus cerebri, 

 forming its fasciculated portion. 



2. The olivary fasciculus divides in the pons into two bundles, one of which 

 ascends to the corpora quadrigemina ; the other is continued to the cerebrum with 

 the fibres of the lateral column. 



3. The fibres from the lateral and posterior columns of the cord, with a bundle 

 from the olivary fasciculus, are intermixed with much gray matter, and appear in 



