368 SPECIAL HISTOLOGY. 



the cornea, while others constitute the proper nerves of the 

 iris. The latter accompany the vessels, dividing repeatedly, 

 and with frequent anastomoses, especially in the annulus 

 minor, to the pupillary margin, where their mode of termina- 

 tion is at present unknown. The elements of all these nerves 

 are, in the trunks, of the medium and fine kinds, from 

 0-002 — 0-004/", and in the iris of not more than O'OOl — 

 0'002"'. I have never noticed ganglion-cells in them, nor in 

 the ciliary muscle, where Bochdalek describes them as existing. 



[Some authors, and among them, recently, Bochdalek, 

 believe that they have seen scattered nerves in the choroid — 

 a circumstance that I am unable to confirm from my own 

 observations. Quite recently, Eainey ('Philos. Magaz./ 

 May, 1851, p. 420) describes a transversely striped choroideal 

 muscle, occupying the posterior part of the choroid and ex- 

 tending through its entire thickness in the form of variously 

 decussating layers, which he says may be most easily demon- 

 strated in the eye of the Sheep. I agree with Henle in 

 thinking that these statements rest upon deceptive grounds; 

 at all events, in the situation in question, either in animals or 

 in Man, I can discover nothing like muscular fibres.] 



§227. 



Nervous membrane [retina). — The retina is the innermost 

 of the five tunics of the eye-ball, and is in close apposition 

 with the choroid, though not coextensive with it, ending at the 

 ora serrata in an undulated margin {margo undulato-dentatus 

 s. ora serrata retina), which is very intimately connected, on 

 the one side with the choroid, and on the other with the 

 hyaloid membrane. A continuation of the retina on the ciliary 

 portion of the hyaloid membrane, which is described by many 

 anatomists, does not exist. 



The retina is a delicate membrane ; when recent, almost per- 

 fectly transparent and clear, and after death whitish and opaque. 

 It commences at the point of entrance of the optic nerve, with 

 which it is, in part, continuous. Its thickness at first is 0;1"', 

 but as it extends anteriorly it soon diminishes to , 06 ,// , until 

 ultimately, close to the anterior border of the retina, it is not 

 more than 0-04/" in thickness, and finally terminates quite 



