528 ALLIS. [VoL. XII. 
branchs and in Apoda, as given by van Wijhe, Platt, and the 
Sarasins. In Scyllium and Pristiurus, van Wijhe concludes 
(No. 130, p. 14) that it arises mainly from the dorsal wall of the 
first head cavity, but, in part at least, from an anterior process 
of the ventral wall of that cavity, — the obliquus inferior arising 
from a second posterior process of this same wall, and the rec- 
tus superior and the rectus internus entirely from its dorsal 
wall. In Acanthias vulgaris (No. 90, pp. 83, 86, and 103) Platt 
says that the inferior oblique arises from the dorsal wall of a 
posterior process or constriction of the premandibular or first 
head cavity, the inferior rectus from the posterior portion of 
the dorsal wall of the remaining portion of the cavity, and the 
superior and internal recti from its anterior portion. In her 
figures the rectus inferior seems to lie immediately above the 
obliquus inferior, and the inferior branch of the oculomotorius 
runs outward and downward behind it. In larvae of Ichthyo- 
phis the rectus inferior overlaps internally the obliquus inferior 
(No. 108, Fig. 72). Whether the head cavities here referred to 
belong to the somites or to the visceral arches is unimportant 
for my purpose, provided the muscles of the eye in the Cyclo- 
stomata and Gnathostomata are of homologous origin, which 
no one would, I think, venture to question. 
We thus see that, in so far as the muscles innervated by the 
inferior branch of the oculomotorius are concerned, the Cyclos- 
tomata and Gnathostomata represent two totally distinct and 
different lines, and that they must both have descended from a 
prototype in which there was but a single muscle, or muscle 
mass, innervated by the nerve in question. Assuming a single 
muscle to have been first formed it was probably an obliquus, 
that muscle being still, in the adult Petromyzon, the largest of 
all the muscles of the eye. We accordingly arrive at a proto- 
type for all fishes, in which the oculomotorius would innervate 
but three muscles, the superior and internal recti by a supe- 
rior branch running forward above the optic nerve, and the 
inferior oblique by an inferior branch running downward in 
front of the rectus superior, and then forward below the opti- 
cus. This would leave the inferior and external recti to be 
innervated by the abducens, as they are in Petromyzon, and 
