152 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
The labium, the largest of the mouthparts, is cylindrical, with a 
deep furrow along the dorsal surface. It terminates in a median 
ligula and two lateral labellae. The labellae are moved by small 
muscles, labellar muscles (Annett and Dutton, : 01 ), from the walls 
of the distal part of the labium itself. The organ as a whole is not 
well provided with muscles. Proximally, the dorsal angles where 
it meets the head, receive fibers from the double retractor muscles 
and on the ventral border the maxillo-labial muscles arise. It is 
probable that the return of this organ to position after the dis¬ 
placement during blood sucking, is accomplished without the activ¬ 
ity of muscles. The lumen of the labium is traversed by the two 
labial tracheae and by two nerves (li n) derived from the infra- 
esophageal ganglion of the brain. 
The remaining muscles of the head fall into two groups : those 
associated with the various parts of the alimentary canal, and those 
supplying other organs. The former class will be discussed in con¬ 
nection with the parts of the alimentary canal which they supply. 
The latter group may be briefly noted. Each antenna receives scat¬ 
tered fibers from the frons and two large muscles from the “head” 
of the tentorium. One of these, the inner antennal muscle, is 
inserted on the inner angle of the base of the antenna. On contrac¬ 
tion it must tilt the antenna forward and inward. The other mus¬ 
cle, the outer antennal muscle, is inserted on the outer posterior 
angle of the base of the antenna and hence on contraction must tilt 
the antenna backward and outward. This muscle is especially large 
in the male mosquito. On the outer face of either tentorium is 
inserted a slender muscle which enters the head through the occipi¬ 
tal foramen. The muscles of this pair may be called the tentorial 
muscles and they correspond to a muscle labeled “ retractor of the 
maxilla ” by Nuttall and Shipley in their figure 23 on plate 8, and to 
the “salivary muscle” of Christophers (: 01 ). The “retractor max¬ 
illae ” in the remaining figures given by Nuttall and Shipley is the 
retractor of the maxilla of my series. The subocular muscles are a 
pair of minute muscles that arise on the floor of the epicranium 
nearly 0.1 mm. behind the bases of the tentoria and are inserted on 
the struts near the origin of the protractors of the maxillae. These 
muscles Avere not recognizable in the specimen from which figures 
on plate 13 were drawn, but have been inserted in two instances 
(figs. 10 and 11) from another series of sections. 
