546 ALETS, [VoL. XII. 
is naturally derived from some such arrangement as that shown 
in the hypothetical proto-urodele type which lies intermediate 
to and below the two great divisions of Pisces. 
II. MUSCLES INNERVATED BY THE TRIGEMINUS AND 
FACIALIS, AND THE NERVI TRIGEMINUS, FACIALIS, 
ACUSTICUS, AND LINEAE LATERALIS VAGI. 
The muscles included in this group are in part innervated by 
the trigeminus alone, in part by the facialis alone, and in part 
by nerves formed by the fusion of branches of both those 
nerves. Whether, in the latter case, the muscles concerned 
are innervated by the facial elements, or by the trigeminal, I am 
unable to determine ; the muscles of the group are, therefore, 
placed for convenience in three separate sub-groups. 
1. Sub-group 1. Muscles innervated by the Trigeminus alone. 
a. Adductor Mandibulae. 
The adductor mandibulae (Figs. 29-42, Pls. XXVI-X XX) 
is a large and complex muscle having an extended surface of 
origin and several different insertions. It has three main divi- 
sions: a superficial one Az, an inner or deeper one A3, and a 
mandibular one Ao. 
The superficial portion Az is much the largest of the three. 
It lies immediately underneath the postorbital bones, and is 
exposed when those bones and the thick tough dermis extend- 
ing from their hind margins to the outer edge of the preoper- 
culum are removed. Its outermost fibres present a fan-like 
appearance, radiating approximately from the coronoid process 
of the mandible and spreading out through somewhat more than 
aright angle. The lower, posterior fibres run, from their origin, 
forward and slightly upward, and the upper, anterior ones for- 
ward and downward, the most anterior ones turning inward at 
the front edge of the muscle and running downward and slightly 
backward along its inner surface. 
The muscle has an extended surface of origin. Its super- 
ficial fibres arise, above, from the postorbital process and 
