130 



LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



2. Below it the fasciculus longitudinalis posterior, and 

 external to this 



3. The fibres of the posterior commissure. 



4. The fibres from the striae medullares thalami. 



5. The red nuclei in the midst of the tegmentum, and spring- 

 ing from them the superior or anterior cerebellar peduncles. 



6. The lemniscus. 



7. The pedunculus corporis mamillaris. 



8. Fibres from the deep marrow near the median line. 



9. Fibres from the stratum intermedium. 



Before reaching the region of the pons, the red nucleus 



begins to diminish in size, the an- 

 terior cerebellar peduncles arising 

 from them pass more and more 

 toward the periphery, and here 

 form two thick, white strands, which 

 lie between the region of the red 

 nucleus and the fillet. In Fig. 75 

 we see the first traces of them at 

 B, and in sections made a little 

 farther back, but which still pass 

 through the corpora quadrigemina, 

 they are already found somewhat 

 farther toward the periphery (Fig. 

 76). In Fig. 77, which represents 

 a section through the velum medullare posticum, they form the 

 outside margin of the cut. Soon after this they pass into the 

 cerebellum. 



The region which is left unoccupied by the disappearance 

 of the red nucleus is filled in by the increasing fibres of the sub- 

 stantia reticularis, which we shall study later on. 



The aqueduct, as before stated, becomes expanded into the 

 fossa rhomboidalis. The gray matter surrounding it also 

 increases in area. A new nerve-nucleus, that of the nervus 

 trochlearis, is met with in this region. Its fibres, however, do 



FIG. 75. 



Commencement of the pons and 

 the decussation of the cerebellar 

 peduncles. S, anterior cerebellar 

 peduncles ; L, fillet of a newborn 

 child. The medullary fibres of the 

 tegmentum are stained with haema- 

 toxylin. 



