278 



ANATOMY OF THE CENTRAL NERYOUS SYSTEM. 



* Posterior to the region of the previous section, the separate elements found in 

 the regio subthalamica and in the tegmentum, which is here increasing, lie so closely 

 upon one another that, for the most part, they are not separable without staining 

 and magniiication. In the illustrations found farther front in the text, much will, 

 therefore, be clearer than in Fig. 179; see especially the figures from the dog. 



The thalamic ganglia are almost entirely blended together. Only the form of 

 the cells and degenerative changes now allow the separation of special nuclei. The 

 nucleus lateralis and the nucleus ventralis have gained the most in expanse; the 

 mesial and the anterior nucleus have entirely disappeared. Here, close to the en- 

 trance into the aqueduct, the layer of central, ventricular gray matter increases in 

 thickness also. Just outside of it appear the "sagittal nuclei of the interbrain": 

 the nuclei of the posterior longitudinal bundle. Then follows laterally the red, teg- 

 mental nucleus, and, in the place where the corpus subthalamicum was situated in 

 the last section, the substantia nigra. The first-named ganglion has dwindled to a 



Corpus callus 



FornW 



Psalterium 



TiEnia 



Nucl. med thai 



Nucl. post. Jong, bdj 



Tegmental nucleus 



Subst. nigia 



Pes peduncuU 



— Nucl. caud. 



- N. lat thai. 

 _Capsuja Inl. 



Insula 



N. vent. thai. 



Lam. med. ext. 



Region of thalamic fillet 



Corp. subthai. 



Inf. thalamic pedicle. 



Opticus 



Comm. ant. 



Nucl. caud. 



Cornu Ammon. 



Lob temp. 



Fig. 179. — Section through the regio subthalamica. 



small remnant which lies farther laterally. In the clear field ventral to the thal- 

 amus there are gathered: fibers from the most posterior territory of the fiber-sys- 

 tems of the corpus striatum, forming a capsule around the red nucleus and entering 

 into it in part; then fibers of the tracts of the lamina medullaris externa; and, 

 separated from this by gray matter, in the most ventral thalamic nucleus, the fibers 

 of the superior fillet. The internal capsule contains, in this situation, substantially 

 the tegmental radiation to the thalamus and tracts from the posterior region of the 

 temporal lobe to the thalamus, also tracts from the same source to the pes pedun- 

 culi — that is, to its lateral portion. 



Ventral to the putamen, here considerably diminished, there is recognized the 

 radiation of the commissura anterior in the neighborhood of the inferior horn. Into 

 the inferior horn itself the most anterior part of the cornu Ammonis is now seen 

 to infold and project. The roof of the inferior horn here also contains the tail of 

 the nucleus caudatus, which is curved downward, and then, naturally, the fiber- 



