248 H. W. NORRIS 
have been traced with absolute certainty, so that with a few 
exceptions, due to imperfect sections, the innervation of each 
neuromast on the head has been traced. 
THE OLFACTORY NERVE 
The olfactory nerve is double in origin and distribution. A 
posterior series of rootlets, arising from the olfactory glomeruli 
in three groups, dorsal, lateral and ventral, produces a nerve 
trunk that is distributed chiefly to the anterior nasal epithelium 
and Jacobson’s organ (fig.1,/p.). The nerves supplying the lat- 
ter structure (Jjo.) apparently enter the ventral group of rootlets, 
but do not comprise the entire group. An anterior series of 
rootlets (Ja.), arising mostly from a single group situated laterally 
on the olfactory lobe and at the inner border of the trunk formed 
by the posterior series of rootlets, innervates chiefly the posterior 
nasal epithelium. In addition, the anterior series possesses a 
small ventral rootlet that arises on the ventro-lateral border 
of the lobe. Into this small ventral rootlet the nervus terminalis 
enters. The nerve, formed by the anterior series of rootlets, 
leaves the brain on the inner border of the other trunk and al- 
most immediately curves over the dorsal border of the latter in 
passing to its destination. It cannot be said, however, that the 
two trunks are absolutely distinct in origin and distribution. <A 
horizontal section through the origin of the nerve from the olfac- 
tory lobe shows that there is some commingling of fibers of the 
two groups of rootlets (fig. 2.). The Caecilians seem to be the 
only other amphibians in which a double olfactory nerve has 
been reported, although Lee (’93, pp. 10, 11) has pointed out the 
double nature of the olfactory lobe. According to Wilder (’91, p. 
689) the olfactory nerve of Siren enters the nasal ‘capsule 
through a large foramen in the ethmoid bone”’ (orbitosphenoid). 
In specimens 140 mm. in length the writer finds the olfactory 
nerve passing through a notch at the anterior end of the orbito- 
sphenoid, but in older individuals of 180 mm. length the orbito- 
sphenoid completely surrounds the exit of the nerve. Wilder’s 
statement that the fibers of the olfactory nerve ‘‘take a direction 
almost laterally outward from the brain, thus lying nearly at 
