SHARK’S EYE, 339 
“ The next muscles which appear are the anterior and posterior oblique, 
which require no particular description. 
“ The remaining muscles are four recti, which arise from and envelope a 
cartilaginous fulcrum, first to be described. A cylindrical, dense, cartilaginous 
body, about two inches long, and of the diameter of a crow’s quill, arises 
from the bottom of the socket and passes straight to the centre of the ball. 
Its extremities, which are rounded, articulate with the socket and the 
sclerotica by cartilaginous cup-like cavities, and are confined to them by 
capsular ligaments. The recti muscles arise tendinous from the fulcrum 
close to its articulation with the orbit ; from thence they diverge on all sides 
the fulcrum, and are inserted by broad tendinous expansions into the 
sclerotica. f 
“ The optic nerve passes through the orbit full the fourth of an inch from 
the origin of the fulcrum, but converging unites with it on entering the 
sclerotica.” 
Such is Mr. Radkin’s description of the structure of the eye of a shark 
recently dead. 
On examining the eye, preserved in spirit, I find that its covering 
externally is of a fine scaly texture, resembling in all respects, excepting 
in the minuteness of the scales, the skin of the animal ; interiorly it is lined 
with a delicate, membrane, as fine and soft as that which lines the eyelids 
of any other animal. This organisation would seem to belong rather to an 
eyelid than a nictating membrane. 
The straight muscles consist of two lateral, and one superior, and one 
inferior. They arise very distinctly from the cartilaginous stem ; the su- 
perior and inferior at more than the fourth of an inch above its articulation 
with the socket. Each of the lateral, although also arising from it, send 
down, epecially the posterior one, a prolongation of tendon for insertion 
into the orbit. In the sclerotica they are inserted at equal distances around the 
globe of the eye, behind the transparent cornea. This disposition of the 
straight muscles of the shark’s eye obviously prevents the cartilaginous body 
assisting their action as a lever so much as has been supposed. 
The oblique muscles arise near each other in the anterior part of the orbit, 
the superior passing obliquely downwards, and the inferior obliquely upwards. 
Their office is to rotate the eye on its axis. ' In ordinary action, they pro- 
bably affect only the articulation of the cartilaginous stem with the globe of 
the eye ; but where the greatest extent of motion is requisite, they may 
* x x 2 
