go 
MAMMALIAN ANATOMY 
eyelid, to determine whether the specimen is from the right or the 
left side. Note form and size of the eyeball, the point of attach¬ 
ment; of the optic nerve, and places of insertion of the various 
muscles. Remove these together with the associated fat and 
connective tissue. Note that the outer wall of the eye ball con¬ 
sists ;of a thick, tough, whitish, skeletal structure, the sclera, 
except in the region where the transparent cornea, resembling in 
life a watch crystal, takes its place on the exposed surface. 
Through the cornea the colored iris with a circular opening in the 
middle, the pupil, may be seen (cf. living eye), and through the 
pupil the crystalline lens, also perfectly transparent in life, but 
rendered opaque by preserving fluids. 
With the specimen under water carefully cut the wall of the 
eyeball along an equator which separates posterior from anterior 
halves, and thus open into the posterior chamber back of the lens. 
Note the §omewhat jelly-like vitreous humor filling this cavity, 
and the delicate retina lining it (frequently detached in the process 
of dissection); the latter, composed of nerve tissue, is the receptive 
organ for light stimuli (cf. microscopic study, pp. 63,64). Note the 
“blind spot” where the optic nerve enters. Outside of the retina, 
between it and the sclera, is the deeply pigmented chorioid layer. 
In the anterior half of the eyeball note the extent of the retina. 
The crystalline lens will be seen supported by a suspensory cap¬ 
sule from the circle of ciliary processes borne on the ciliary fold 
which lies between the chorioid and the outer circumference of the 
iris. Draw an internal view of ( 1) the posterior and (2) the anterior 
half. ; 
The small anterior chamber, filled with a watery fluid, the 
aqueous humor, lies in front of the lens and may be opened into 
from behind by carefully removing the lens and its capsule. This 
exposes the ciliary fold and the inner surface of the iris, in which 
there are both radiating and circular muscle fibers. Draw the 
interior of the anterior half with the lens removed. 
External Study of the Living Eye and Its Surroundings in 
the Human Subject. —Note eyebrows, eyelids supported by 
tarsal; cartilages and fringed with eyelashes; the thin skin (con¬ 
junctiva) which lines the eyelids and covers the front (exposed) 
surface of the eyeball; by turning back the eyelid, the outlines of 
