516 THE SOLIDS. 



implanted, passing in this course across the line of the an- 

 terior chamber and through the aqueous humour. They are 

 seen more easily in some animals than in others, forming a 

 regular series of pillars around the anterior chamber." 



It would appear, however,that these fibres, which may be 

 readily detected in the human eye, should rather be described 

 as proceeding from the schlerotic, and passing, some on the 

 anterior surface of the elastic lamina, and others on the front 

 of the iris, thus assisting in uniting these parts to that tunic ; 

 it is very doubtful whether they have any structural connec- 

 tion with the posterior elastic lamina. (See Plate LXVIIL 



fig- ) 



The ciliary nerves pierce the ciliary muscle on their way 

 to the iris. 



Retina. 



We come in the next place to the description of the most 

 interesting and important of the many structures which 

 enter into the composition of the globe of the eye, namely, 

 the retina. This membrane may be regarded as the expan- 

 sion of the optic nerve, to which certain other structures 

 are superadded, and, like most of the other membranes of 

 the eye, is divisible into distinct lamella? ; these, reckoning 

 from without inwards, are, tunica Jacobi, or " stratum bacil- 

 losum," the granular or nuclear layer, the ganglionary layer, 

 the vesicular layer, the fibrous expansion of the optic nerve, 

 and, lastly, the vascular expansion of the arteria centralis 

 retina?. 



The tunica Jacobi is composed of a single stratum of cells of 

 very remarkable form. They are minute in size, several times 

 longer than broad, having their long axes disposed vertically 

 to the general surface of the retina, and they each consist of 

 a body or head of a more or less globular or oval shape, and 

 of a prolongation or tail, four or five times longer than the 

 head, and not more than a third of its diameter. By their 

 coherence these cells form a distinct membrane, the heads of 

 the cells all being directed one way, namely, towards the 



