620 



LECTURE XXIV. 



224 



Sepia officinalis. 



membrane of tlie aqueous humour, and is finally continued into the 

 groove of the crystalline lens (j^). 



The space between the eye- 

 ball and its capsule, thus cir- 

 cumscribed, is filled with an 

 aqueous humour, by which 

 the cornea is separated from 

 the eyeball, and kept tense. 

 The outer tunic of the proper 6 

 eyeball is a fibrous mem- 

 brane (d) covered by the ^ 

 aponeurotic expansion of the 

 muscles of the eye, and with 

 an anterior aperture which is 

 closed by the crystalline lens. 

 Within the fibrous tunic there 

 is a thin cartilaginous coat (e) 

 perforated posteriorly by the 

 numerous fibrils from the optic ganglion (gg). The layer of fibrous 

 membrane (m) is continued from the anterior margin along with the 

 outer fibrous layer {i) to form the pupillary aperture {n), which is en- 

 croached upon by a bilobed process analogous to the curtain, which de- 

 pends from the iris of the ray. The cartilaginous sclerotic is lined by a 

 thick expansion of the nervous fibres given off* from the optic gan- 

 glion. These fibres are sent off" from the outer surface of the ganglion, 

 which presents a pulpy texture in its centre. They are grouped 

 into flattened bundles, which decussate each other before perforating 

 the cartilaginous sclerotica, and, after expanding into the retina (o o), 

 extend towards the groove of the crystalline lens, and, being joined 

 by a thin membrane from the anterior margin of the cartilaginous 

 sclerotic, it forms a ciliary plicated zone {p p), which penetrates the 

 groove of the crystalline lens. 



The inner surface of the retina is covered by a layer of dark pig- 

 ment {q), which is penetrated by the papillae of the retina. The 

 vitreous humour has a distinct and strong hyaloid coat. The crys- 

 talline lens is of large size, and consists of two distinct parts ; the 

 anterior or smaller moiety being the segment of a larger sphere, and 

 the posterior that of a smaller sphere : they are separated by delicate 

 transparent membranes continued from the ciliary body. The lens 

 presents the same denticulated fibrous structure arranged in con- 

 centric laminas, as in the higher animals. 



The large optic ganglion {f) is imbedded in a white lobular sub- 

 stance (/i), which defends it from the pressure of the muscles of the 



