500 ALETS: Vor sunk 
representing the anastomosis of the two arteries described by 
Wright in Lepidosteus (No. 133, p. 484). Continuing forward 
the efferent pseudobranchial artery crosses under the rectus 
externus, turns upward behind and above the rectus inferior 
but under the nervus oculomotorius, and reaches the orbit. 
It then turns outward and forward, internal to and then above 
the inferior branch of the oculomotorius, and lying immediately 
behind the optic nerve, enters the eyeball with that nerve, behind 
and a little above it, through the large opening in the carti- 
laginous sclerotic (0f, Fig. 24, Pl. XXIV). It is the arteria 
ophthalmica of Sagemehl (No. 104, p. 203), and gives rise, accord- 
ing to Wright (No. 133, p. 495), to the dorsal part of the choroid 
gland. During its course through the orbit it is enclosed in a 
tough fibrous envelope, which, in the large fish used for illustra- 
tion, had become, either naturally or through the action of 
reagents, semi-cartilaginous in character and appearance, and 
formed a tough, elastic, tube-like structure extending from the 
cranium to the eyeball. Sagemehl found no trace of a choroid 
gland in Amia (No. 106, p. 116). 
Two other vessels (ov and ov’, Figs. 22-27, Pls. XXIV and 
X XV) extend from the cranium at the hind end of the orbit to 
the eyeball, and, in the one large fish, they were, like the arteria 
ophthalmica, semi-cartilaginous in appearance. They are both 
of them veins, though they have, even in larvae in sections, 
much the appearance of arteries. The smaller of the two, ov’, 
issues through a perforation in the sclerotic near its outer edge, 
between the insertions of the rectus superior and the rectus 
externus, and runs downward, backward, and inward between 
those two muscles to join a large vein, the orbital sinus of 
Parker in Mustelus, which lies along the side of the skull imme- 
diately below and internal to the ophthalmic branch of the 
trigeminus. From this orbital vein, distal to the point where 
it is joined by the vein ov’, a branch, the anterior cerebral vein 
of Parker in Mustelus (No. 83, p. 712), was traced in embryos 
through the cartilage of the side of the skull into the brain cav- 
ity, where it was distributed to the fore-brain and the olfactory 
nerve. In the adult this branch was not traced ; the foramen by 
which it leaves the skull was, however, always found, lying some- 
