SECT. 114.] NERVOUS SYSTEM. 227 



latter place the cells are pigmented and beautifully branched . 

 The pons Varolii contains, besides the just-mentioned gray masses, 

 which in part belong to it, numerous collections of gray substance 

 in its interior, with smaller and larger multipolar cells, which are 

 so irregularly imbedded between the white fibres, that they do not 

 admit of a detailed description. 



It is a difficult matter to ascertain the relations of the ten pairs 

 of nerves, which come from the medulla oblongata, the pons and the 

 cerebral peduncles. But few inquirers have endeavoured to solve 

 this question by other than the usual means; that is to say, by 

 following the fibres with the knife, which is not all-sufficient here. 

 Among these exceptions are E. Weber, who employs preparations 

 hardened in carbonate of potash, and Stilling, who uses alcohol- 

 preparations. The results which I myself obtained by chromic- 

 acid-preparations, which were mostly rendered transparent by 

 caustic soda, agree in almost every respect with those of Stilling, 

 to whom we are indebted for a very beautiful work on the medulla 

 oblongata and the pons. The ten posterior cerebral nerves arise 

 without exception, not from the columns or collections of fibres 

 from which they pass out, but all penetrate more or less deeply 

 into the central parts, and all, probably, become connected (some 

 not till they have decussated, like the trochlear is and probably the 

 Inipoglossus and accessorius) with definite parts of the gray sub- 

 stance, which Stilling not inaptly calls nerve-nuclei. It is espe- 

 cially the floor of the fourth ventricle, and the aqueduct of Sylvius, 

 which are concerned in these origins, seeing that all the nerves in 

 question extend at least partially to them. For particulars, see 

 Stilling's work and my Micros. Anatomy, ii. pp.458 — 462. 



§ 114. The Cerebellum, in the distribution of its elementary 

 parts, presents rather simple relations, grey substance occurring 

 only upon the surface of the convolutions, in the nucleus dentatus, 

 and upon the roof of the fourth ventricle; all the rest consists 

 of white substance. The latter is made up solely of parallel, 

 probably unbranched, dark-bordered nerve-tubes, which possess 

 all the characters of central tubes. As far as can be ascertained, 

 they present almost everywhere essentially the same relations, 

 and measure from cooi 2" to 0*004'" i* 1 diameter, their mean 

 diameter being 0'002'". The grey substance exists, 1, very 

 sparingly upon the roof of the fourth ventricle, above the velum 

 medullar e inferius, in the form of brown cells, of 0'02''' to 0"03"' 

 in size, scattered in the white substance, and readily recognisable 



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