392 ' THE ALIMENTARY CANAL OF THE IMAGO. 
Kraepelin terms these muscles the retractors of the proboscis; their con- 
traction causes the lower end of the fulcrum to describe a circular arc, and 
brings it into a horizontal position between the gene. : ; 
2. The Retractors of the Rostrum.—Each of these muscles arises from 
the inferior lateral margin of the occipital foramen. They are long and 
slender. They lie one on either side of the middle line, behind the lingual 
salivary duct; they are inserted into the sesamoid sclerites. 
. 3. The Accessory Retractors of the Rostrum arise with the preceding, 
and lie behind them; they are inserted into the integument about midway 
between the sesamoid sclerites and the head capsule. These two pairs of 
muscles serve to invaginate the integument of the rostrum, when the 
proboscis is withdrawn into the head capsule. 
4, The Flexors of the Haustellum arise from the inferior edge of the 
occipital foramen, between the retractors of the rostrum, and are inserted 
into the dorsal surface of the prepharyngeal tube. They serve to flex the 
haustellum upon the rostrum. 
5, The Extensors of the Haustellum arise from the distal cornua of the 
fulcrum, and ascend and are inserted into the great apodéme of the labrum. 
6. The Retractors of the Haustellum arise from the gen, and are 
inserted with the extensors of the haustellum. Kraepelin thinks that these 
and the last act together, and so, by pushing down the apodéme of the labrum, 
straighten the proboscis by extending the haustellum on the rostrum, This 
appears to be probable. 
7. The Flexors of the Labrum arise from the anterior surface of the 
fulcrum, and are inserted into the labrum. They undoubtedly flex the 
haustellum on the rostrum. In those Diptera in which the labrum can be 
raised independently of the haustellum they serve to open the mouth. 
8. The Retractors of the Fulerum.—These are small bundles of muscle 
fibres which arise from the lower part of the frontal sac, and which are in- 
serted into the muscular coat of the cesophagus between the fulcrum and the 
brain. They serve to draw the loop of the cesophagus, which lies between the 
cephalic ganglia and the fulcrum, forward, when the proboscis is retracted 
into the head capsule. These fibres are not described by Kraepelin. 
9. The Graciles, a pair of long and very slender muscles, arise from the 
proximal extremity of the fulcrum, and descend behind it to the valve of the 
lingual duct. Their contraction evidently opens this valve. All the above 
muscles lie in the rostrum and head capsule. 
A single muscle occupies the cavity of the fulcrum in front of the pharynx ; 
it is the 
10. Dilator Pharyngis.—This muscle arises from the lateral plates of the 
fulcrum, and its fibres converge and are inserted into a median raphé on 
the dorsal plate of the pharynx; its action is to dilate the pharyngeal tube. 
It is undoubtedly the main agent in drawing fluid from the mouth into the 
pharynx. : 
The muscles of the haustellum are: 
1. The Retractors of the Furca.—A pair of large muscles which arise, 
one on either side, from the upper half of the thyroid sclerite; the Abres of 
each are inserted into a tendon, which is attached to the corresponding lateral 
