554 



THE CEREBETJM. 



rated by a network of delicate connective tissue, consisting of cells 

 possessing distinct nuclei and delicate processes, which unite to form 

 incomplete laminae. 



The general direction which the fibres follow is best seen in a brain that has 

 been hardened by immersion in alcohol, although it is true that in an ordinary- 

 dissection of such hardened masses with the scalpel, we do not then trace the 

 single fibres, but only the smaller bundles and lamellre which they form by their 

 aggregation. It must also be admitted that where thoy intimately decussate, the 

 tearing of fibres across is liable to be mistaken for the separation of sets of fibres 

 one from the other ; it is necessary to correct such errors by the examination of 

 sections under the microscope. The microscopic examination of the cerebrum, 

 however, is as yet still less complete than that of the spinal maiTOw and medulla 

 oblongata. By the dissection of artificially prepared brains, aided in part by 

 microscopic observ^ation, the following general facts have been ascertained. 



The fibres of the cerebrum, though exceedingly complicated in their 

 arrangement, and forming many different groups, may be referred to 

 three principal systems, according to the general course which they take, 

 viz. : — 1. Ascending or pedimcniar fibres, which pass from the medulla 

 oblongata to the hemispheres, and constitute the peduncles of the cere- 

 brum. These fibres increase in number as they ascend through the 

 pons, and still further in passing through the optic thalami and 

 striated bodies, beyond which they spread in all diiections into the 

 hemispheres. 2. 2'ransverse or commissural fibres, which connect the 

 two hemispheres together. 3. Longitudinal or coJMeral fibres, which, 

 keeping on the same side of the middle line, connect more or less 

 distant parts of the same hemisphere. 



1. The Peduncular fibres, in each hemisphere, consist of a main 

 body and of certain accessory bundles of fibres. 



Fig. 387. — Posterior View 

 Fio-. 387, ^^ '^^^ Peduncles of the 



°' ' Cerebrum and Cerebel- 



lum (after Arnold). 7^ 



The loT/er and fore part of 

 the cerebral hemispheres is 

 preserved, tbe cerebellum is 

 completely detached from its 

 peduncles, and on the right 

 side the corpora quadrigemina 

 and thalamus opticus have 

 been dissected, a, fasciculus 

 teres of the left side ; h, fibres 

 of the tegmentum ascending 

 through the right thalamus ; 

 r, left corpora quadrigemina ; 

 d, lateral column of the cord ; 

 c, restiform body ; /, superior 

 peduncles of the cerebellum ; 

 g, fibres of the crust ; i, i, 

 the fillets ; k, k, corpora 

 striata ; I, the left thalamu-; ; 

 m, m, sections of the middle 

 peduncles of the cerebellum ; 

 n, section of the left inferior 

 peduncle ; p, left posterior 

 pyramid ; q, section of the 

 corpus callosum ; s, under 

 surface of the same, and below it the cavity of 'he fifth ventricle ; e, left anterior pillar 

 of the fornix ; y, decussation of the radiating fibres with the crossing fibres of the coi-pus 

 callosum. 



