472 
• Head of Psylla mali 
(a) A group of five muscles runs from the occipital sclerite obliquely to the 
latero-ventral portion of the thorax. 
( b) A group of three muscles runs from the occipital sclerite through the 
neck to the dorsal margin of the prothorax. 
(a) and (b) serve to retract the head. 
(e) A short stout muscle attached in front to the side of the neck, and 
behind to the ventral margin of the pronotum. 
(d) A short stout muscle attached to the neck, in front, at about the same 
point of attachment as (c), but passing closer to the side of the body, and joins 
on to the dorsal surface of the side of the prothorax. 
(c) and (d) control the movements of the head upon the neck. 
VII. The Muscles of the Oral Region. 
(a) A muscle attached to the gena anterior to the buccal cavity, traverses 
the head into the prothorax and joins on to the postero-lateral margin of the 
labial furrow. 
(a) serves to further depress the head. 
( b ) A small muscle attached to the gena at the same point as (a) but 
passes obliquely upwards and is attached to the dorsal portion of the side of 
the body. 
(c) A muscle attached to the dorsal surface of the buccal fold, traverses 
the head, and passes to, and becomes continuous with, the dorso-lateral 
margin of the labial furrow, close to the point of attachment of (a). 
(d) A small muscle runs obliquety upwards between the outer lateral 
margins of the buccal fold and the dorso-lateral portion of the body. 
(e) A small muscle runs from the lateral margin of the buccal fold almost 
horizontally forwards to the side of the body. 
These muscles (b-e) regulate the movements of the sclerites surrounding 
the mouth. 
VIII. The Muscles of the Labium. 
(a) The elevator muscles. A long, slender muscle attached at its lower end 
to the first joint of the labium at a point where it originates on each side of 
the setal chamber, runs obliquely upwards and forwards and becomes con¬ 
tinuous with the side of the body. 
The contraction of this muscle elevates the proximal portion of the first 
joint of the labium, retracting it further into the labial furrow. 
(b) The muscles of the terminal joint. In the expanded portion of the second 
joint of the labium, two pairs of muscles are present, one pair on each side of 
the groove, attached at their lower ends to the junction of the bulbular ex¬ 
pansion on the anterior face of the second joint with the terminal joint, and 
stretching obliquely upwards, join on to the posterior wall of the labium at a 
much higher point. 
From their position, these muscles can only control the movements of the 
