384 



GENERAL STRUCTURE AND FUNCTIONS 



nected with the remaining parts by the olfactory commissures. The 

 separation of the hemispheres (2, 2) shows the corpora striata (3) and 

 the optic thalami (4). Then come the tubercula quadrigemina (5), 

 which are here composed, as above mentioned, of four rounded 

 masses nearly equal in size. The cerebellum (e) is considerably en- 

 larged by the development of its lateral portions, and shows an 

 abundance of transverse convolutions. It conceals from view the 

 fourth ventricle and most of the medulla oblongata. 



In other species of quadrupeds the hemispheres increase in size 

 so as to project entirely over the olfactory ganglia in front, and to 

 cover in the tubercula quadrigemina and the cerebellum behind. 

 The surface of the hemispheres also becomes covered with nume- 

 rous convolutions, which are curvilinear and somewhat irregular 

 in form and direction, instead of being transverse, like those of the 

 cerebellum. In man, the development of the hemispheres reaches 

 its highest point ; so that they preponderate altogether in size over 

 the rest of the ganglia constituting the brain. In the human brain, 

 accordingly, when viewed from above downward, there is nothing 

 to be seen but the convex surfaces of the hemispheres ; and even 

 in a posterior view, as seen in Fig. 126, they conceal everything 

 but a portion of the cerebellum. All the remaining parts, how- 

 ever, exist even here, and have the same connections and relative 

 situation as in other instances. They may 

 best be studied in the following order. 



As the spinal cord, in the human subject, 

 passes upward into the cranial cavity, it en- 

 larges into the medulla oblongata as already 

 described. The medulla oblongata presents 

 on each side three projections, two anterior 

 and one posterior. The middle projections 

 on its anterior surface (Fig. 130, i, i), which 

 are called the anterior pyramids, are the con- 

 tinuation of the anterior columns of the cord. 

 They pass onward, underneath the transverse 

 fibres of the pons Varolii, run upward to the 

 corpora striata, pass through these bodies, 

 and radiate upward and outward from their 

 external surface, to terminate in the gray 

 matter of the hemispheres. The projections 

 immediately on the outside of the anterior pyramids, in the medulla 

 oblongata, are the olivary bodies (2, 2). They contain in their in- 



Fig. 130. 



MEDULLA 

 OF H r M A N 



OBLONOATA 

 BRAIN, ante- 



rior view 1, 1. Anterior py- 

 ramids. 2, 2. Olivary bodies. 

 3,3. Restitbrra bodies. 4. De- 

 cussatiuu of the anterior co- 

 lumns. The medulla oblonj:- 

 ata is seeu terminated above 

 by the transverse fibres of the 

 pons Varolii. 



