276 ANATOMY OF THE CENTEAL NEETOUS SYSTEM. 



does not regard the fornix as terminating in tiie corpus mamiliare, but thinlis that 

 after crossing through the same it goes, via the deeussatio hypothalamica, into the 

 opposite thalamus, where it is said to end within the ventral nuclear groups. 



By means of the substantia nigra, the fiber-systems which pass down- 

 ward from the forebrain and interbrain are divided into two parts, which 

 differ as to their physiological significance, the pes, or crusta, and the 

 tegmentum. 



Now let us briefly consider the glandula pinealis (conarium), or 

 epiphysis, which, with its pedicles running on the inner side of the thalamus, 

 represents a portion of the roof of the interbrain (see Figs. 20 and 21). 

 It consists essentially of solid epithelial tubules, which have originated 

 through proliferation of the primary evagination. 



The conarium contains, in addition to the tubules and an abundant 

 blood-supply, the hrain-sand : small concretions of a stratified structure, 

 which consist principally of calcium-salts and of a small organic basis. 



The position of the glandula pinealis, at the posterior end of the thala- 

 mus and between the corpora quadrigemina, is shown in Fig. 125. 



I would like to remind you again of what was said on page 127 about 

 the significance of the conarium in reptiles. 



Fibers appear to extend as far as the conarium from the tracts of the taenia 

 thalami. The taenia rises anteriorly by the side of the fornix from the depth of the 

 olfactory field and, after it has received an afferent tract from the fornix, ends in 

 the ganglion lialicnnhr after it has passed along the mesial edge of the thalamus. 

 The ganglion is located just in front of the epiphysis (see Fig. 177). The posterior 

 portion of the bundles of the taenia is also designated as the pcdiiiicuU conarii. 

 Between the two pedunculi conarii runs the delicate cominissiira habenularls, prob- 

 ably a decussating tract from the tfeniae habenulte (very clearly shoAvn in transverse 

 section in Fig. 144) . It is also to be noted in Fig. 144 how the glandula pinealis, 

 almost massive in man, appears in the rabbit to be an evagination of the roof of the 

 forebrain and passes over into the plexus chorioideus. 



Precisely as in the lower vertebrates, so in mammals, a large tract passes down 

 to the base of the midbrain from the ganglion habenula;. It is the tractus habenulo- 

 pediincukiris. 



I will now take up again the demonstration of the brain-sections that 

 ■was interrupted at the close of the last chapter. They are intended to assist 

 you in reviewing and studying what has just been presented, and to serve 

 as a means of orientation. The section shown in Fig. 178 follows directly 

 upon that of Fig. 174. 



Located just behind the ehiasma, the section sho^s, on the one hand, the 

 thalamus in its greatest breadth; on the other, as an important factor, the emerging 

 of the fiber-systems of the internal capsule at the base of the brain as the fiindaiiicnt 

 of the prs, or crusta. Between the pes and the thalamus is situated the regio subtha- 

 lamica, and new ganglia lie in this. Note the "ganglion of the zona ineerta," the 

 corpus sublhalamicum (Luys), and ventrally the group of ganglia of the corpus 



