188 ANATOMY OF THE CENTRAL NEEVOUS SYSTEM. 



tuberance is called the tuber cinereum, its cavity the infundibulum. In Fig. 

 125 it is not visible, but may be seen in the median section shown in Fig. 

 133 and in front of the chiasma {lam. t.) in Fig. 135. 



The fissure between the thalamus and the nucleus caudatus is traversed 

 by a long vein, beneath which is constantly found a slender tract of white 

 fibers: the stria terminalis, or tmnia semicircularis. Isolated depressions 

 may be more or less distinctly recognized on the surface of the thalamus. 

 They separate from one another the elevations which correspond to the 

 thalamic ganglia. 



The tuberculum anterius, the arched surface of the nucleus anterior 

 thalami, is always demonstrable. The line of division between a mesial and a 

 lateral thalamic nucleus is also pronounced at times. The entire thalamus is 

 covered vri-thin by the central gray matter, which is connected for a short 

 distance with the gray matter of the opposite side to form the commissura 

 mollis. At the extreme anterior end the pillars of the fornix dip into this 

 gray matter. Near the place where this occurs a small bundle of fibers is 

 seen on each side to ascend from below, reach the surface of the thalamus, 

 and pass backward close to its mesial edge. It then passes, anteriorly to the 

 midbrain, for the most part into an elongated body, the ganglion hdbenulce, 

 on the dorsal edge of the thalamus. The bundle is called the twnia thalami, 

 and,forms an afferent pathway, passing from the olfactory apparatus at the 

 base of the brain to the interbrain. 



A part of the tsenia, receiving other fibers on its way, passes farther 

 backward posterior to the ganglion habenula?, and then runs to the other 

 side directly in front of the pineal body. The portion between the ganglion 

 and the pineal body is called the pedunculus conarii, because the body 

 appears to rest on it. 



The decussation of the bundles lying just in front of the epiphysis is 

 designated as the commissura liabenularum . This decussation lies directly 

 dorsal and anterior to the commissura posterior, from which in most eases it 

 is not separated at all (see Fig. 144 also). 



The gray mass of the thalamus is overlaid by white fibers, the stratum 

 zonale, which, in part, pass into the optic nerve. An enlargement of the 

 posterior portion of the thalamus, the pulvinar, forms the chief point of 

 origin of these nerves. The largest part of the optic nerve disappears in this 

 ganglion and in a protuberance which lies on its under side: the corpus 

 geniculatum laterals. 



The tracts of nerves from the hemispheres, which were situated deep 

 down between them and the interbrain, emerge in great part from the cere- 

 bral mass posteriorly to the interbrain, and then lie exposed as two thick 

 strands on the under surface of the midbrain. Taken together, they are 

 called the crui'a of the brain, or the pedunculi cerebri. 



