No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 495 
lateral end of the pad, the optic nerve, which runs outward, 
forward, and slightly downward, along the upper, shelving sur- 
face of the cartilaginous bar, pierces the lining membrane of 
the optic fenestra and enters the orbit. 
The hind edge of the optic fenestra (ofn, Figs. 9 and 11, PI. 
XXI) is formed by the pedicle of the alisphenoid, the bone 
being always, in the specimens I have examined, cut out behind 
by the large trigeminal foramen, so as to leave a pedicle, and 
not simply perforated by it, as described by Sagemehl. The 
pedicle thus formed rests externally upon a process of the lat- 
eral wing of the parasphenoid, and internally upon a cartilagi- 
nous base which forms part of the side wall of the eye-muscle 
canal. Between this cartilaginous base and the pedicle exter- 
nally, and the lining membrane of the eye-muscle canal and the 
thin, projecting plate or fin of the alisphenoid internally, there 
is formed a tall and relatively narrow opening by which the 
eye-muscle canal communicates with the orbit. Along the bot- 
tom of this opening, which may be called the orbital opening 
of the canal, the rectus externus enters the main, lower portion 
of the eye-muscle canal, and in its upper part the trochlearis, 
oculomotorius, and ophthalmicus profundus issue from the 
upper, lateral chamber of that canal and enter the orbit. 
The upper, lateral portion or chamber of the eye-muscle canal 
(emc') lies in a recess in the side wall of the cranium, the 
recess extending from the pedicle of the alisphenoid back to 
that process of the petrosal that forms the front wall of the 
utricular fossa. This chamber has in addition to the tall, 
narrow opening just described, which is common to it and the 
main eye-muscle canal, five openings leading to the outer sur- 
face of the cranium, namely: the large facial foramen (//7) 
through the petrosal; the small foramen for the external 
carotid (ecfr) immediately below and in front of that foramen 
and through the same bone ; the otic canal (ofc) leading to the 
top of the skull through the cartilage in front of and above the 
petrosal; the large trigeminal foramen (¢/7) through the edge 
of the alisphenoid, immediately behind and lateral to the pedicle 
of the bone; and the smaller foramen for the ophthalmic 
nerves (offr) through the alisphenoid immediately above and 
