72 LECTURES ON THE CENTRAL NKRVOUS SYSTEM. 



which can be plainly seen on the median surface of the hrain, 

 is shown in Fig 1 . 42, with the help of which yon will easily be 

 able to form a general idea of the distribution of the fibres of 

 this body. Only the fasciculus, called the tapetum, does not 

 belong to the corpus callosum, as was formerly thought. It is 

 present in cases where the corpus callosum is wanting (Kauf- 

 mann, Onufrowics). In those cases it is apparent that it is the 

 caudal radiation of the fasciculus arcuatus. 



Near the floor of the third ventricle a second mass of fibres 

 passes transversely across in front of the anterior ventricular wall 

 and the crura of the fornix. This is the anterior commissure. 

 It cannot be traced on a cross-section, as is shown in the partly 

 diagrammatic Fig. 41. Its fibres are much more curved, inas- 

 much as they pass arch-like through the corpus callorrum on each 

 side, curving downward and backward, and are lost in the 

 white substance of the temporal lobe. In Fig. 46 this arch has 

 been cut through, on both sides, external to and below the nu- 

 cleus lentiformis. A part of the anterior commissure, which is 

 only slightly developed in human beings, but strongly developed 

 in lower animals, connects the two points of origin of the olfac- 

 tory nerves (olfactory-lobe division of the anterior commissure). 

 It is the little bundle which passes downward into the- gray 

 matter in Fig. 41. 



From every part of the cerebral cortex numerous fibres 

 arise, w T hich connect the cortex with the deeper-lying portions 

 of the central nervous system. Very many pass into the thala- 

 mus, others may be traced to the gray masses of the raid-brain 

 and to the nerve-nuclei of the pons, in which they seem to ter- 

 minate. A number pass farther back through the 'capsule, the 

 cms ccrebri, the pons, and the medulla oblongata to the 'spinal 

 cord, where they enter the gray matter at different levels. 



Taken together, these fibres which pass downward from 

 the cortex are called the corona radiata. You will form no bad 

 idea of these if you can imagine the thalamus placed free under 

 the overarching dome of the cortex, and then assume that fibres 



