THE CORPUS CALLOSUM. 



757 



a out is to l>e made through it on the right side about half an inch 

 from the middle line ; and this is to be extended forwards and 

 hack wards, as far as the limits of the underlying ventricle. While 

 utting through the corpus oallosum, the student may observe that 

 a thin membranifortn structure (ependyma) lines its under surface. 



Tin' corpus callosum is thicker at each end than at the centre, in Is thickened 

 Alienee of a greater number of fibres being collected from the ateachend ! 



for . Man . 



firn'ns 



trtmsu.jass. 



pineal stria 

 post, comm. 

 pineal bodu 



i , tab. ualu 



uuiua \ 



pyramid 



FIG. -274. PORTION OF A MEDIAN SECTION OF THE BRAIN, SHOWING THE CORPUS 

 CALLOSUM, THIRD (3) AND FOURTH (4) VENTRICLES. ARBOR VITJB CEREBELLI. &c. 



In front of 3, the soft commissure 

 is seen cut across. Between the in- 

 f u ml ib iilum and the corpus albicans 

 the tuber cinereuru, and behind the 

 corpus albicans the posterior per- 

 forated space and the united teg- 

 menta are forming the floor of the 



third ventricle. Above 4, is the 

 superior medullary velum with the 

 lingula upon it, and below are the 

 inferior medullary velum and the 

 nodule. The pia mater and velum 

 interpositum are removed. 



cerel >rum in those positions ; and the posterior part is the thickest under 

 of all. Connected with its under surface along the middle at su 

 the fore part is the septum lucidum or partition between the 

 ventricles (fig. 274), and behind is the fornix. 



This i* the chief commissural body of the halves of the cerebrum, 

 and its fibres pass laterally into the medullary centre of the hemi- 

 sphere, in which they radiate to the convolutions. 



Dissection. The left lateral ventricle is to be now opened in Dissection, 

 the same way as the right ; and to prepare for the examination of 



