FIBRES OF THE CEREBRUM. 



775 



which pass from before backwards, uniting together part8 of the 

 same hemisphere. The chief bands of this system which the 

 student can recognise are the following : The fornix, the tsenia 

 semicircularis, the pineal stria, the longitudinal stria of the corpus 

 callosum, and the cingulum. Other fibres pass in the medullary 

 centre between adjoining and more distant convolutions, describing 

 arches beneath the sulci : these are known as the association-fibres. 



Dissection. The dissector may now make a transverse section 

 of the remains of the left hemisphere at the fore part of the optic 

 thalamus, when the form and relations of the lenticular nucleus 

 and the claustrum, together with the position of the anterior 

 commissure, will be apparent (fig. 279). 



Cuts should also be made into the geniculate bodies to show the 

 grey nuclei within them. 



By dividing transversely the left half of the midbrain through 



known as 



association 



fibres. 



Make 



sections of 



lenticular 



nucleus, 



geniculate 

 bodies, 



and raesen- 

 cephalon. 



FIG. 283. TRANSVERSE SECTION- OF THE UPPER PART OF THK MIDBRAIN 

 (AFTER OBERSTEIXKK). 



the superior quadrigeminal body, there will be seen the grey matter 

 of that eminence, the crusta and tegmentum separated by the sub- 

 stantia nigra, the red nucleus of the tegmentum, and the grey 

 matter of the Sylvian aqueduct (fig. 283). 



Finally, if the student has been working with two brains, he 

 should make a longitudinal section through the remains of the 

 pons, medulla and cms, passing a shade to the left of the middle 

 line, and on examining the cut surface below the floor of the fourth 

 ventricle and below the grey matter in the floor of the remains of 

 the Sylvian aqueduct he will see a small, longitudinally running, 

 band of white fibres coming up from the deeper parts of the 

 medulla. This is the posterior longitudinal bundle, which chiefly 

 consists of fibres running between the motor nuclei of the medulla, 

 pon.s and midbrain. 



Lougitudi- 



nfeduj 1 1 ^ 

 and pons ; 



posterior 



