365 



direction ; so that they form a considerable layer around the commis- 

 sure, through which, by numerous fissures, they radiate to its oppo- 

 site surface. This fibrous and inner layer is crowded with round 

 and oval nuclei like those found at the border. Now when the epi- 

 thelium is followed to the pineal gland, the substance of the latter is 

 seen to be composed of elements which resemble it so closely, and 

 are so uninterruptedly continuous with it, that one can scarcely ques- 

 tion the probability that the two kinds of structures are only slight 

 modifications of each other. The pineal gland consists of fibres, 

 nuclei, and the well-known brain-sand. The fibres are arranged in 

 two ways ; throughout the gland they form, by peculiar subdivisions 

 and communications, an intricate network, in which the nuclei are 

 lodged. Some of them are exceedingly fine, others rather coarse, 

 but bear no resemblance to what we are accustomed to call nerve- 

 fibres. They are frequently crooked, and apparently jointed or dilated 

 at intervals, where they give off branches which bear nuclei ; in other 

 places the nuclei are surrounded by flat riband-like fibres. Here and 

 there the fibres of the network go off to form straight bundles, which 

 unite into larger trunks, and have chiefly a transverse direction. The 

 reticular structure bears a decided resemblance to the epithelium of 

 the olfactory mucous membrane, and still more to what I have else- 

 where described as the fourth layer of the olfactory bulb in the 

 Sheep, and particularly in the Cat. 



In the pons Varolii the decussation between fibres from the opposite 

 sides is extremely complicated. In a direction from behind forwards 

 there is a series of decussations : 1. Between fibres of the superior 

 peduncles of the cerebellum ; 2. Between some of the inner fibres of the 

 fillet as they descend obliquely to the medulla oblongata ; 3. Between 

 fibres proceeding from the corpora quadrigemina behind the crura 

 cerebri ; 4. Between fibres proceeding from the floor of the iter a 

 tertio ad quartum ventriculum and the nucleus of the third nerve ; 

 and, 5, Between numerous fibres of the crura cerebri, as they enter 

 the upper end of the pons Varolii. 



In the substance of the pons Varolii, and resting on the outer and 

 back part of the cylinder formed by the superior peduncle on each 

 side, there is a short but thick cylindrical column of large multi- 

 polar cells, pierced by a number of longitudinal bundles, and con- 

 nected by fibres with the nucleus of the third nerve. It commences 



