INTERNAL ANATOMY. 121 



posterior end of the abdomen. Among the Tyrogly- 

 phidse by far the most mobile mandibles are those 

 of the genus Histiostoma ; where these organs are in 

 constant and rapid, alternate, saw-like action, and the 

 muscles are naturally modified to suit this. 



The posterior of the two systems is that of the 

 retractor muscles of the rostrum (mrr) ; these in 

 Hericia are probably the longest muscles in the body, 

 and mostly arise about over the posterior end of the 

 supra-oesophageal ganglion ; but some of the lateral 

 bundles arise further back. The tendons of the more 

 central of these muscles are inserted into the hinder 

 edge of the rostrum, but Nalepa says that in Carpo- 

 ylyphus some, probably the lateral bundles, are inserted 

 into the corners of the maxillary lip. All these 

 muscles serve to withdraw the rostrum into the came- 

 rostrum. 



There are other muscles attached to the rostrum; 

 which has almost universal, although rather slight, 

 motion. The muscles which serve as flexors of the 

 rostrum arise, according to Nalepa, from below the 

 pharynx ; and are inserted into the hind margin of the 

 lip. There are also some small muscles which serve to 

 give a slight revolving movement to the rostrum, and 

 which arise partly from the sternum and partly from 

 the anterior epimera and sclerites. 



The muscles which work the moveable arm of the 

 chela of the mandible are contained within the mandible 

 itself ; the powerful occlusor muscles (mdo) arise from 

 the inner side of the upper surface and the upper part 

 of the posterior surface of the chitinous exterior of the 

 mandible, and are inserted into the upper proximal 

 angle of the moveable arm of the chela. The weaker 

 divaricator muscles (mdd) arise from the lower part of 

 the posterior surface, and are inserted into the lower 

 proximal corners of the moveable arm. 



There is but little special musculation accompanying 

 the maxillae. Nalepa says that in Carpoglyphus ano- 

 ni/mus each of what he calls the " Kaulade," which is a 



