THE EYEBALL AND ASSOCIATED STRUCTURES IN 
THE BLINDWORMS. 
H. W. NORRIS. 
Incidental to a more extended investigation of coecilian anat- 
omy the following observations were made upon the ocular 
muscles and nerves. 
Typically two groups of muscles are attached to the eyeball 
in vertebrates : a rectus group of four muscles, dorsal, ventral, 
lateral and medial ; and an oblicpie group of two muscles, dorsal 
and ventral. The dorsal, ventral and medial rectus and the ven- 
tral oblique muscles are innervated by the oculomotor ; the dor- 
sal oblique is supplied by the trochlear nerve, and the lateral 
rectus by the abducens. This is the arrangement in a shark and 
in man. In some other cases there is a retractor bulbi muscle 
of the eyeball. In such forms as the cat, dog and ox the re- 
tractor bulbi is in four slips, which in their insertion alternate 
with the four rectus muscles. It is quite commonly stated in 
works on the anatomy of the domestic animals that the retractor 
bulbi is innervated wholly or in part by the oculomotor nerve. 
Hopkins has recently shown that such statements are wholly in 
error, the muscle always being innervated by the abducens nerve. 
In many of the amphibians we see another muscle related to the 
movements of the eyeball, a levator bulbi muscle, innervated 
by a branch of the mandibular ramus of the trigeminal nerve. 
In the coecilian amphibians the optic apparatus is always 
more or less rudimentary or modified. Two distinct types occur. 
In the one the eyeball is situated beneath the maxillary bone; 
the optic nerve and all the eye-muscles and eye-muscle nerves, 
except the retractor bulbi and its nerve, the abducens, have 
completely disappeared. The retractor bulbi becomes the re- 
tractor muscle of the tentacle. In the other type the eyeball is 
situated just beneath the skin, and while rudimentary is never- 
theless probably affected by light. Some or all of the eye- 
muscles and their nerves may be present, but for the most part 
in a vestigial condition,, or modified for purposes other than op- 
tical. 
In Herpele ocliroceplialum we have an example of the first 
type. The large retractor tentaculi is innervated by the sixth 
