373 ANATOMY OF THE CENTRAL NERVOUS SYSTEM. 



intermingle, and decussate, a region containing gray masses which are them- 

 selves again filled, in part, by a fine net-work of small decussating, medul- 

 lated fibers. 



Fig. 175 shows some of the details of a section through this region. Below the 

 thalamus is a roundisli ganglion, the nucleus tegmenti, the red nucleus of the 

 tegmentum; external to this there has appeared the corpus subthalamicum (nucleus 

 of Luys), which has a somewhat lenticular form. Posteriorly, the nucleus tegmenti 

 will appear much larger in the transverse sections. It is the point of origin of a 

 large bundle, the peduncle, or Tr. tegmento-cerebellaris, which passes to the op- 

 posite half of the cerebellum. Ventral to it, and mesial to the corpus subthalamieum, 

 there is found a third ganglion, the sulistantia nigra Someringi, an accumulation of 

 nerve-cells which are mostly pigmented with gray. This is also better developed in 

 the more posterior planes. It lies directly over the fiber-systems from the internal 

 capsule, which now become the pes. 



From the regio subthalamica on down as far as the end of the midbrain this 

 dark-grayish ganglion may always be demonstrated above the pes. 



There terminates in the substantia nigra, designated as the stratum intermedium 

 ■pediijiciiU, the last remnant of the fiber-system from the corpus striatum. 



Between the ventral niiclens of the thalamus and the ganglia men- 

 tioned there pass a great many convergent white fibers. They arise from 

 several sources, and also have an approximately stratified disposition; so 

 that the individual layers may be separated somewhat.- Nevertheless, "de- 

 generation" preparations -were the only ones on which the discrimination 

 could be clearly made. Farthest lateral lie the tracts of the tegmental path- 

 way destined for the ventral, thalamic nucleus. It has long been believed 

 that some of them turned directly downward to the afterbrain, and this 

 part was designated as the superior, or cortical, fillet. Even now this view 

 is maintained on some sides (see my older Fig. 168, also). But in the last 

 few years it has been successfully shown that the fiber-tract from the cortex 

 terminates in the thalamus, that, however, a new pathway arises from this, 

 the tractus ilialamo-buTbar'is , the superior fillet, which may be followed down- 

 ward as far as into the nuclei of the posterior columns. Tliis is a portion 

 of ilie sensory pathway, of luhich ive now knoiu tivo parts: the cortico-thalamic 

 ■and the thalamo-oUongatal parts. Ending extraordinarily near to one an- 

 other, both must be in intimate contact within the ventral thalamic nucleus 

 (Monahoiu, Mahaim, Bielschofshy). 



The superior, or upper, fillet is found, on the sections illustrated, ven- 

 tral to the thalamus and near to the nucleus tegmenti. But it is separated 

 from this by means of a thick meduUated bundle, the tractus cortico-teg- 

 mentalis, the coronal bundle of the tegmental nucleus (Dejerine). Laterally 

 the superior fillet and the coronal bundle form a true medullary capsule 

 around the nucleus tegmenti: the lamina medullaris nuclei tegmenti. 



The radiations to the tegmental nucleus and to the superior fillet do not 



