CH. XLVI.] SECTIONS OF PONS AND MID-BRAIN 671 



by deeper transverse fibres, which constitute what is known as the 

 trapezium (f). These fibres belong to a different system, and form 

 part of the central auditory path ; some of them connect the auditory 

 nuclei of the two sides together. The larger olivary nucleus is no 

 longer seen, but one or two small collections of grey matter (o.s.) repre- 

 sent it and constitute the superior olivary nucleus. These as well as a 

 collection of nerve-cells in the trapezium (nucleus of the trapezium) 

 are connected with fibres of the trapezium, while some of their axons 

 pass into the adjacent lateral part of the fillet. 



The nucleus of Deiters (n. VII L, fig. 413) begins to appear in the 

 upper part of the bulb, and extends into the pons ; it lies near the 

 floor of the ventricle, a little mesial to the restiform body. The 

 nerve-fibres connected with its cells pass towards the middle line, 

 and enter the posterior longitudinal bundle, which is more clearly seen 

 in the two next sections (fig. 414). This bundle of fibres connects 

 Deiter's nucleus, the nucleus of the third and sixth nerves, and the 

 anterior horn cells of the spinal cord. The fibres which pass into it 

 from Deiters' nucleus bifurcate, one branch passing upwards to 

 arborise around the cells mainly of the oculo-motor nucleus of the 

 opposite side ; the other extends downwards through the bulb into 

 the cord, where they are found in the antero-lateral descending tract 

 of each side. They end by synapses around the anterior horn cells. 



This bundle receives in addition to the fibres from Deiters' nucleus, other fibres 

 from the sensory nucleus of the fifth nerve, and from large cells in the reticular for- 

 mation of mid-brain, pons, and bulb. 



The nerves which are connected with the grey matter of this 

 region of the pons are the sixth, seventh, and eighth, as shown in the 

 diagram. The nuclei in connection with the fifth nerve are higher 

 up, where the floor of the ventricle is again narrowing. At last, in 

 the region of the mid-brain, we once more get a canal (Sylvian 

 aqueduct) which corresponds to the central canal of the spinal cord. 



Fifth and Sixth sections are taken through the mid-brain, and 

 are drawn on a smaller scale than the others we have been examin- 

 ing ; they represent the actual size of the sections obtained from the 

 human subject. 



Near the middle is the Sylvian aqueduct, with its lining of ciliated 

 epithelium. In the grey matter which surrounds it are large nerve- 

 cells from which the fourth nerve, and higher up the third nerve, 

 originate ; the fibres of the third nerve are seen issuing from these in 

 fig. 414, R, III. The reticular formation of the pons is continued up 

 into the mid-brain, and is called the tegmentum. It is composed of 

 both longitudinal and transverse bundles of fibres intermingled with 

 grey matter. Its transverse fibres include those of the superior 

 peduncles of the cerebellum which decussate in the middle line (fig. 

 414, A, S.C.P.). 



