290 



NORMAL HISTOLOGY. 



bundles become once more collected into two compact strands, which are 

 continued into the crusta of the cerebral peduncles. The dorsal limit of the 

 ventral field is occupied by the stratum profundum pontis, a well marked 

 layer of deep tranverse fibres. A considerable amount of gray matter, col- 

 lectively known as the pantile nucleus, is distributed within the interstices 

 between the bundles of nerve-fibres. The numerous cells of this nucleus 

 (Fig. 337), generally small in size and stellate in form, are related to the 

 ponto-cerebellar fibres of the same and of the opposite side, many being 

 stations of interruption in the cortico-cerebellar paths. 



The dorsal or tegmental part of the pons resembles in its general 

 structure to a considerable extent the formatio reticularis grisea of the 



FIG. 338. Section across pons at level D, Fig. 329; i, pyramidal tracts; 2, transverse fibres ; 3, decus- 

 dtion and (4) arm of superior cerebellar peduncle ; 5, nucleus and (6) descending root of V nerve ; 7, 

 ray matter surrounding (8) Sylvian aqueduct ; 9, 10, n, parts of IV nerve and its decussation ; n, lateral 

 llet ; 13, posterior longitudinal fasciculus ; 14, tegmental area ; 15, mesial fillet. X 3. (Preparation by 



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medulla, consisting for the most part of a reticulum of transverse and longi- 

 tudinal fibres, interspersed with nerve-cells, on each side of the median 

 raphe. The appearance of certain masses of gray matter and of nerve- 

 fibres, together with changes in the position of the fillet, produces details 

 that vary with the level of the section. When this passes just above the 

 lower margin of the pons (Fig. 336), two diverging and obliquely cut 

 strands of fibres mark the root-fibres of the sixth and seventh cranial nerves 

 and divide the tegmental region, on each side, into three areas. The 

 middle area, between the abducent fibres mesially and the facial ones 

 laterally, contains three important collections of nerve-cells. One of these, 

 the nucleus of the sixth nerve, lies close to the floor of the ventricle and 

 near the mid-line. The axones of these neurones, the root-fibres of the 

 abducent (sixth) nerve, take an oblique ventral path and cut through not 



