DEVELOPMENT OF EAR AND ACCESSORY ORGANS IN FROG. 537 
sule winding past the posterior ampulla, and lying above the 
hinder part of the utriculus. The remainder of this canal 
passes through a foramen in the lower, inner, and hinder part 
of the wall of the capsule (foramen rotundum), and extends 
back within the brain-case till it reaches and communicates 
with the previously described canal. The part-within the skull 
is of considerable size, occupying the lower angle on each side, 
and thence it extends up the side wall for some distance, and 
along the floor nearly to the median line. 
The course of these two canals will perhaps be rendered 
intelligible by fig. 19. This figure is diagrammatic and com- 
pounded from a large series of sections. By this method 
the whole course of the system is shown, though it is fore- 
shortened, so that structures are brought into view that could 
not be cut in one section. Turning now to the other forms in 
which I have found these structures, I will show that two 
very similar canals exist in all, though their mutual relations 
vary. 
The toad I have only examined in a young stage just after 
the tail is lost, but I have no reason to doubt that at this time 
the adult arrangement obtains ; for in frog tadpoles of only 25 
mm. in length, these canals have attained to the permanent 
condition in all essential points. The toad only differs from 
the frog in the fact that the first canal never leaves the pro- 
tection of the auditory capsule in its course to the skull. It 
runs through a special foramen immediately behind the second 
canal and in a position similar to, but somewhat lower than, 
its point of exit, and so directly into the skull. Within the 
skull both join as in the frog, and from this common part a 
large diverticulum runs down through the glossopharyngeal 
foramen, and occupies a position similar to the corresponding 
part in the frog. Thus the frog and the toad agree except 
in the relative positions of the foramina through which the 
first cana! and the glossopharyngeal nerve pass. 
Dactylethra I have cut as a small larva, the legs being 
present but as yet neither large nor pentadactylous. In this 
specimen the perilymphatic spaces are present and connected 
