THE SUBTIIALAMIC REGION, ETC. 



Ill 



point it contains the following tracts: 1. The fibres from the 

 motor region of the cortex, which we have learned to know as 

 the pyramidal tract in both the corona radiata and the internal 

 capsule. They lie near the middle and are slightly shaded in 

 the cut. 2. The fibres from the frontal lobe to the pons, situ- 

 ated internal to the pyramidal tract. 3. The fibres from the 

 occipital lobe to the pons. They are situated external to the 

 pyramidal tract. Above these three divisions of the pes pedun- 

 cu'li, of which the first mentioned earliest receives a medullary 

 covering, are found fibres apparently from the corpus striatum, 

 which are not designated in the cut (compare Fig. 50), Mey- 

 nert's stratum intermedium, and 

 then comes the substantia nigra, an 

 of fine nerve-fibres and 



FIG. 63. 



Commencement of the pons in a 

 newborn child. Hsematoxylin stain- 

 ing. Decussation of the cerebellar 

 peduncles. 



oo o 



ganglion-cells whose significance is 

 whollv unknown. External to this 







(</, in Fig. 62) lies another little 

 ganglion, which, so far as I know, 

 has never been described. 



In the te^mentum you will at 



O 



once notice the two large, round, 

 gray bodies ; they are the red nuclei 

 (compare Fig. 59) ; the corpus sub- 

 thalamicum, which is shown near it 

 in Fig. 54, has disappeared when we reach this level. 



The red nucleus, which receives fibres from the thalamus 

 (and tegmental radiation ]), is, at this point, i.e.. under the cor- 

 pora quadrigemina, very rich in medullary fibres. These pass 

 under the posterior quadrigeminal body toward the middle line, 

 and decussate with the fibres of the opposite side. They belong 

 to the superior peduncles of the cerebellum. The decussation 

 is called the decussation of the superior cerebellar peduncles. 

 It is shown in Fig. 63. Farther back the crossed cerebellar 

 pedunculi develop into thick bundles of fibres, which lie external 

 to the red nucleus ; they gradually attain a still more external 



