438 SPECIAL HISTOLOGY. 



at first sight appears to be a continuation of the basis of the 

 cerebral peduncles passing below and external to the optic 

 thalamus, between the lenticular and caudate nuclei of the 

 corpus striatum, to enter directly into the medullary substance 

 of the hemispheres. Closer observation renders it obvious, 

 that this white substance, as has been said before, in part 

 enters the corpus striatum, particularly the lenticular nucleus, 

 and in part radiates from without inwards, from the hemisphere 

 into the optic thalamus. That is to say, very numerous white 

 fasciculi, visible even to the naked eye, coming from the 

 hemisphere throughout the entire height of the thalamus, enter 

 the latter, run towards the superior surface to the superior 

 and internal border, and the pulvinar, being ultimately 

 lost exactly in the same way as are the fibres continued from 

 the crus cerebri into the corpus striatum; that is, these 

 fasciculi, the elementary fibres of which originally measure 

 0*0012 — 0*0025'", ultimately subdivide into extremely close 

 plexuses composed of fibres of the most extreme fineness, 

 0*0004 — 00008'", the terminations of which cannot be traced. 



I will just notice the constitution of some structures 

 connected with the above-described ganglia. The substantia 

 nigra of the crus cerebri presents pigment- cells precisely similar 

 to those of the substantia ferruginea, except that they are for 

 the most part rather smaller, and have feiver processes, sur- 

 rounded with nerve-fibres of the finest, and also of the stronger 

 kind. The commissura mollis contains smaller cells, with 

 1, 2, 3, and more processes, and light coloured pigmentary 

 contents ; and besides these, very many, plexiform, vertical, and 

 horizontal, fine fibres of 0*0012 — 0*0016'", with some still finer, 

 less than 0*001'", and a few stronger measuring as much as 

 0-004'". The pineal gland exhibits pale, rounded cells, without 

 any processes, and scattered nerve-fibres of - 001 — 0*002'", 

 and also, generally, a considerable quantity of sabulous matter 

 (brain-sand) (vid. § 118). Its peduncles, their anterior pro- 

 longations, and the commissura jjosterior, contain fibres mea- 

 suring 0*001 — 0*003'", and are composed in part also of the 

 finest fibres. The floor of the third ventricle presents, imme- 

 diately beneath and behind the anterior commissure, extremely 

 large, and smaller, colourless cells, with from one to four, 

 occasionally very thick processes. These are lodged in great 



