A. D. Imms 
105 
The remaining muscles of the head which have yet to be dealt 
with are those belonging to the mouth-parts (Fig. 2), and the most 
prominent of them are the muscles of the mandibles. 
Each mandible is moved by a pair of stout muscles, an adductor, 
which is attached to its inner angle, and an abductor attached to its 
outer angle. The adductor muscle is the stouter of the two and 
consists of four separate bands of fibres (a.m.). Three of these arise 
from the wall of the head-capsule a short distance behind and below 
the eyes, but the fourth band arises separately at a point somewhat in 
front of the places of origin of the former, and, moreover, it is ventro¬ 
lateral in position. The four bundles pass upwards and inwards, 
converging as they do so, and are inserted into a stout chitinous process 
from the mandible. The abductor muscle similarly consists of four 
distinct bands or bundles of fibres ( ci'.vi '.), two of these arise close to 
the three dorsal bands of the adductor while the other two take their 
origin near to the ventral bundle of the latter. 
Attached to about the middle of the base of each maxilla are a pair 
of muscle bands ( mx .). If these be traced backwards they are seen to 
run in close proximity to each other, and their points of origin are 
situated ventro-laterally on the cranial wall, near to those of the ventral 
bands of the abductor muscle of the mandible. 
The labial plate is provided with a pair of depressor muscles; they 
are attached on either side near to the base of that organ where it 
becomes confluent with the ventral surface of the cranium, and converge 
as they pass forwards to their points of insertion. 
Owing to the imperfect transparency of the head-capsule it has not 
been possible to fully study the movements of the various muscles in the 
living larva. Their functions, as implied by the names here given, have 
been largely inferred from a study of their relations to the different 
parts principally by means of serial sections. 
The muscles of the thorax. In the thorax there is a well developed 
system of longitudinal muscles arranged in a dorsal and a ventral series. 
The dorsal series, or longitudinal tergal muscles, lie a short distance 
beneath the integument and occupy much of the mid-dorsal area above 
the digestive canal. The ventral series, or longitudinal sternal muscles, 
form two groups, one on either side of the nervous system. Immedi¬ 
ately in front of the prothoracic ganglia, a transverse muscle baud 
crosses over the nerve cord and unites together certain of the longi¬ 
tudinal sternal muscles. Tergo-sternal muscles are also present, aud 
the most anterior of them is a stout muscle which takes origin from 
