CRANIAL NERVES OF SIREN LACERTINA 295 
surface of the. head. Posteriorly these neuromasts in a surface 
view are not distinguishable from the postorbital series, but from 
their innervation it is seen that the two series overlap. Wilder 
seems to have overlooked this ramus. 
7. Ramus mentalis externus VII 
From the point of separation of the rami mentalis internus and 
externus the latter passes anteriorly laterally and ventrally over 
the lateral border of the quadrate cartilage and squamosal bone 
to the lower jaw, along the ventro-lateral border of which it runs 
to its final termination (figs. 12, 11, 8,4). It innervates the oral 
series of neuromasts. From the main trunk of the mentalis and 
from the base of the ramus mentalis externus there arise five or 
six small nerves which supply neuromasts widely scattered over 
the side of the head, posteriorly from a short distance anterior to 
the gills nearly to the eye anteriorly, encroaching dorsally upon 
the territory of the occipital, supraorbital and infraorbital series, 
and ventrally upon the gular series. This poorly defined group 
of neuromasts—in fact differentiated from other fields solely by 
its innervation—appears to be the postorbital series, although it 
does not correspond exactly to the series so designated by Kings- 
bury for Amphibia in general. In Amphiuma the writer found a 
small number of nerves arising from the hyomandibular trunk 
and from the base of the ramus mentalis externus innervating a 
widely scattered series of neuromasts, considered by him as the 
postorbital series, although not coinciding with the series so named 
by Kingsbury. It is possible that one or two of the small nerves 
arising from the base of the mentalis internus should be reckoned 
with this postorbital innervation. Kingsbury describes a small 
series of neuromasts, the angular, situated at the angle of the 
mouth and extending upon the upper lip. The writer has shown 
that in Amphiuma these neuromasts, about six in number, are 
supplied by two small branches of the mentalis externus. When 
we seek for corresponding neuromasts in Siren, taking as criteria 
the situation upon the side of the head and extension anteriorly 
upon the upper lip, and the innervation by small branches of the 
mentalis externus given off near the base of the same, we find 
