518 THE SOLIDS. 



This layer is exceedingly thin and delicate, hardly indeed 

 to be considered as a distinct stratum, but yet consisting of 

 numerous caudate ganglionary globules, in every respect 

 similar in point of structure to those which have been de- 

 scribed as occurring in so many of the ganglia of the human 

 brain. 



These caudate cells differ considerably in size, but yet are 

 all referable to one of two standards, the larger very much 

 exceeding the smaller in dimensions. (See Plate LXVIL 

 fig. 8.) . 



It is in the human retina only that these cells have as yet 

 been detected. 



The fourth or vesicular layer lies immediately on the outer 

 surface of the fibrous layer, the cells composing it are several 

 times larger than the nuclei of the granular layer ; a few of 

 the most external of them are granular and nucleated, but 

 the majority, and these the larger cells, are clear and trans- 

 parent as water, perfectly globular, and without appreciable 

 nuclei. The cells of the vesicular layer resemble very closely 

 the delicate cells which have been described in a previous 

 part of this work, as found in the fibrous portions of the 

 human brain. (See Plate LXVIL fig. 7.) 



The fibrous gray layer is best seen and most strongly 

 marked in the retina near to the optic nerve. If a portion of 

 this membrane be cut off and spread out upon glass, it will 

 be seen to present, viewed with the inch or half-inch object- 

 glass, a number of parallel or rather radiating flattened bands, 

 two of which occasionally divide or bifurcate. 



If, in the next place, these bands or bundles, having been 

 separated somewhat from each other by means of needles, 

 and as much, of the granular layer which so obscures them 

 washed away with a camel's hair brush as possible, be then 

 examined, they will each be observed to present a fibrous 

 appearance, and on a prolonged and careful examination it 

 will become apparent that they are made up, first, of a small 

 quantity of nucleated fibrous tissue, and, secondly, and prin- 

 cipally, of gray gelatinous, nerve fibres. (See Plate LXVIII. 

 Jig. 6.) 



