1240 Recent Literature. [ December, 
II. Muscucature AND MOTILE Mecuanism.—t. Movements of 
the basal parts of the Probvscis——There are two pairs of re- 
tractor muscles. One pair arise from the anterior band of the 
cranium (Fig. 4, mr) and are inserted on the inferior suspensor 
processes (zs) of the fulcruin. The other pair arise from the 
postero-basal plate of the cranium and ' reach forward so 
as to be inserted on a cross-ridge (Fig. 3, x) near the end of the 
basi-proboscis. By their contraction they retract the thick wall- 
plate of the labiun telescopically into the basi-proboscis. The 
second pair also flex the hypopharynx on the “small capsule,” 
and the whole labium upon the fulcrum; we may term them 
“flexors of the labium.” 
Fig. 8.—Nerves, etc., of labium. 
Two pairs of weak muscles arise from the sides of the occipital 
foramen. One pair of these aid the unfolding of the marie 
boscis. The other run forward over the “small capsule an 
seem to be inserted in the base of the labrum; they may 
retractors of the labrum. difficult 
| The mode of protruding the proboscis involves a more @ i 
problem, The muscle which Becker describes as drawing 
fulcrum around its hinge, has no existence. The tracheal he 
ratus comes to exercise a powerful influence at this pom ramen 
large air-trunks after entering the head by the occipital a when 
enlarge to form (seemingly two) capacious air-sacs, which, is 
the proboscis is extended, fill all the cranial awy erry: 
occupied by the nerves and the invaginated “ct ak 
(Fig. 1, 4). Y This cranial cavity is serviceable for the retro the 
the proboscis, as by the collapse of the tracheal sacs t ~ for the 
withdrawal of air from the head, a vacant space 1S fe d by me 
reception of the fulcrum, (I renounce the view once ? a 
that the cranial bladder aids in retracting the proboscis. the head 
spiratory mechanism of the trunk by driving air towar® |” rye 
causes the protrusion of the basal parts of the prone 
