fae H. W. NORRIS 
SUMMARY 
A study of the cranial nerves of Siren lends little if any support 
to the view that it is a primitive form. Rather, the opinion 
based upon general considerations of comparative anatomy 
(Driiner ’04; Kingsbury ’05; Emerson ’05; Norris ’11) that the 
perennibranch Urodela are permanent larvae of forms that once 
had a complete metamorphosis, is confirmed. This view has been 
set forth with great clearness by Driiner. The branchial nerves 
and musculature of Siren have an arrangement which can be 
explained satisfactorily only on the hypothesis that it is the result 
of general reduction processes, more or less modified, to be sure, 
by local and restricted specialization. ‘The popular view (Holmes 
’06, p. 3) that “‘the Proteidae constitute the most primitive of the 
Urodeles”’ becomes absolutely untenable from the standpoint of 
comparative anatomy. Primitive amphibian characters are not 
to be sought in larval stages only, temporary or permanent, for 
the larval condition itself is to be looked upon as an amphibian 
acquirement and not an ancestral pre-amphibian character. In 
short, the amphibian larval characters are fish-like only by 
analogy. For a correct interpretation of the anatomy of Siren 
we should ignore its especial larval characters only as we compare 
them with corresponding features of the larvae of other Urodela. 
Though Siren may be the permanent larva of a form by no means 
primitive, yet among its specialized structures and retrograde 
developments, it may be possible, nevertheless, to distinguish 
very significant relationships and perhaps even primitive charac- 
teristics. 
The olfactory nerve in Siren is more distinctly double in origin 
and distribution than in any other urodele amphibian. 
The nervus terminalis seems to have the relations characteris- 
tic of the Urodela. 
The eye-muscle nerves have the typical arrangement, but this 
may be due largely to their imperfect development. 
The levator and retractor antorbital muscles, having their 
insertion on the antorbital cartilage, and their innervation by a 
branch of the ramus mandibularis V, have been described in but 
