THE TELENCEPHALON. 



1185 



strictly commissural ones. Indeed, with the more exact and extended study of the corpus 

 callosum, it becomes more and more evident that the composition and relations of this great 

 bridge are very intricate and complex, and that it receives contributions from a much larger 

 number of and more diverse sources than was formerly recognized. 



The observations of E. A. Spitzka upon the size and sagittal area of the corpus callosum 



have conferred additional „ 



. ^ : ^1 • ^ Fig. 1024. 



mterest upon this struc- 

 ture as a possible index 

 as to intellectual develop- 

 ment. The examination 

 of a series of brains 

 which included some from 

 men of acknowledged 

 intellectual superiority, 

 demonstrated a corpus 

 callosum of unusual area 

 as a constant feature in the 

 brains of the more highly 

 endowed individuals. 

 And, further, that the 

 size of the corpus callo- 

 sum bore a direct rela- 

 tion to the character of 

 intellectual superiority 

 which the individual 

 was known to possess, 

 the largest commissure 

 being found in the brain 

 of a man whose intel- 

 lectual greatness implied 

 the exercise of associa- 

 tion paths to an unusual 

 degree. The later con- 

 clusions of Bean, however, 

 seriously question (consult page 1197) the constancy of the relations above suggested. 



Corpus 

 callosum 



Median long. 



stria 

 Lateral long. 



stria 



Choroid plexus 



Hippocampus, 

 cut obliquely 



Tapetum 



Occipito- 

 thalamic 

 radiation 



long, inferior 



Frontal section of right hemisphere, passinsj just behind splenium of corpus cal- 

 losum ; inferior horn of lateral ventricle is cut obliquely. 



The anterior commissure consists of a compact cord-like strand, slightly 

 compressed from before backward and therefore oval in section (Fig. 996), 

 which connects the anterior ends of the temporal lobes, as \vell as the olfactory 

 bulbs. As it crosses the mid-line, the commissure is placed immediately in front 

 of the downward arching anterior pillars of the fornix, in the interval between 

 which it appears as a white transverse ridge on the narrow anterior wall of the 

 third ventricle (Fig. 979). Its posterior surface is covered with the ventricular 

 ependyma. whilst in front it is in intimate relation with the lamina cinerea 

 (page 1 131). Laterally it arches backw^ard and downward, thq entire commissure 

 forming a il-shaped tract, with the convexity presenting forward, whose ends 

 broaden as they sweep backward into the temporal lobes (Fig. 968). In 

 addition to uniting the fore-parts of the last-named lobes, the anterior commis- 

 sure connects the olfactory bulbs and consists, therefore, of a temporal and an 

 olfactory part. 



The olfactory part is much the smaller and appears as a delicate fasciculus which 

 curves downward and forward to enter the olfactory tract. Its fibres include : ( i ) 

 those which arise in one olfactory lobe and pass to that of the opposite side; (2) 

 those which connect the olfactory lobe with the cortex of the opposite hippocampal 

 convolution ; (3) those which extend from the olfactory lobe through the commis- 

 sure and, joining the taenia semicircularis, proceed with this strand along the roof 

 of the inferior horn of the lateral ventricle to end in the amygdaloid nucleus 

 (page 1 172). ^ . 



The temp07'al part includes the greater portion of the commissure. After pass- 

 ing almost horizontally outward beneath the lenticular nucleus (Fig. 1025) as far 

 as the mesial borders of the putamen, it turns backward and continues its course 

 beneath the lenticular nucleus, where it appears in frontal sections as a transversely 



75 



