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POPULAR SCIENCE REVIEW. 
sclerotic in front of the retina where the corpus ciliare and 
ciliary muscle are placed, is of no great extent. It gently 
rounds off into the region behind it, in a manner not con- 
spicuous externally. The anterior portion of the eye is more 
strongly prominent. 
The basal moiety of the sclerotic is exceptionally small. It 
is constituted by a round cartilaginous disc overlain by a layer 
prolonged from the much larger fibrous portion. This disc 
does not reach the optic nerve.- The anterior zone of the fibrous 
moiety, surrounding the lens, is strengthened by a ring of 
peculiarly curved thin bony plates which are sunk in its 
substance. 
The choroid is very thin, but is notably thickened posteriorly 
throughout the region subtending the yellow spot. A some- 
what conical projecting pecten, about a millimeter in depth, 
covers the place of entrance of the optic nerve. The corpus 
ciliare is broader than the iris and pupil taken together. The 
muscles of the iris are extensive, as in birds ; from the marginal 
sphincter fibres stretch backward towards the ciliary border, 
and behind these is a less powerful radial dilatator. The iris of 
the dead Chamaeleon is half as wide as tho pupil. It lies in 
complete contact with the lens. Its brilliant anterior surface 
has a dark background. Insignificant prominences replace the 
ciliary processes, anterior to which occur exceedingly weak 
meridional flutings. On the outer side of the corpus ciliare the 
ciliary muscle ( tensor chorioidece of Briicke) arises from a con- 
spicuous lamina of connective tissue, which reflects light and 
serves to support the cornea. The relative diameter of the 
cornea is less than in any other vertebrates except the turtles. 
The anterior chamber of the eye,- containing the aqueous 
humour, is remarkable for its slight depth. 
The lens, on the other hand,, is strongly eon vex. 
But of all parts of the eye the retina is most worthy of 
study, because of its large yellow spot. This, the region of 
exact vision, occupies the hinder pole of the retinal concave, and 
displays a central pit surrounded by a far extending zone, 
throughout which the retina is much thicker and beautifully 
modified in its minute structure. Especially modified is the 
so- called percipient layer. 
The corresponding region of the human eye shows this layer 
to be furnished in the fovea proper with cones only. The 
yellow spot around it has many cones and but few rods, while 
in the remainder of the retina the rods greatly outnumber the 
isolated cones. Of two equal retinal areas that which has more 
numerous (and therefore more slender) cones permits more 
precise visual discrimination. Heinrich Muller dwells on the 
