39^ 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 gemc. 



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 proboscis is withdrawn into the head capsule. 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 

 baustellum 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 apoddme of the labrum. 



6. The Retractors of the Haustellum arise from the genrc, and are 

 inserted with the extensors of the haustellum. Kraepelin thinks that these 

 and the last act together, and so, by pushing down the apodeme 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 Uiptera in which the labrum can be 

 raised independently of the haustellum they serve to open the mouth. 



8. The Retractors of the Fulcrum. 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 oesophagus 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 ol 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 rap he' 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 fibres of 

 each are inserted into a tendon, which is attached to the corresponding lateral 



