44 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8l 



of the buccal cavity arise upon the clypeus, and this relation between 

 the region of the buccal cavity and the clypeus appears to be a constant 

 one. In the cicada, the sucking ]5ump is a mouth structure quite 

 distinct from the true pharynx, and the origin of its dilator muscles 

 upon the large striated facial sclerite of the head wall helps to identify 

 this plate as the clypeus (fig. 46 H, Clp). In many insects, however, 

 there is no structural distinction between the region of the buccal 

 cavity and that of the pharynx. The retractor muscles of the mouth 

 angles (fig. 19, ^8) have their origin on the inner surface of the frons, 

 and their points of attachment give another character, in addition to 

 that furnished by the labral muscles, for the determination of the 

 frons when the limits of this sclerite are obscured, or the identity of 

 the plate otherwise doubtful. The mouth retractors are inserted upon 

 chitinous processes that extend into the stomodeal walls at the mouth 

 angles from the suspensorial rods of the hypopharynx (fig. 42 B, y). 

 Usually these processes are short and inconspicuous, but in the bees 

 they form long arms united at their bases in a chitinous plate in the 

 floor of the buccal cavity. 



The region of the pharynx is usually marked by a dilation of the 

 stomodeum, and sometimes it forms an abrupt enlargement of the 

 tube. The frontal ganglion is situated on its dorsal wall (fig. 19, 

 FrGiig), and the circumoesophageal connectives lie at its sides. The 

 dorsal dilator muscles of the pharynx have their origin on the frons, on 

 the parietals, on the dorsal arms of the tentorium, and rarely one or two 

 l^airs may encroach on the area of the clypeus (caterpillars). The 

 pharynx of the Orthoptera is divided into an " anterior pharynx " and 

 a "posterior pharynx" (Eidmann, 1925), but the part called the 

 posterior pharynx, the dorsal dilator muscles of which arise on the 

 posterior dorsal walls of the head, appears to correspond with the 

 oesophageal region in some other insects. 



The oesophagus, when there is a distinct oesophageal region, is a 

 narrow tubular part of the stomodeum following the pharynx (fig. 

 19, OE). and varies much in length in dififerent insects. Its posterior 

 end enlarges into the crop (Cr), or the crop is sometimes a lateral 

 diverticuhun. The terminal part of the stomodeum in biting insects 

 is usually a well-defined proventriculus (Pveiit). The chitinous 

 intima of all parts of the stomodeum may be provided with short hairs, 

 spicules, or chitinous nodules, but the inner cuticular structures are 

 best developed in the proventriculus. where they generally have the 

 form of longitudinal ridges or ])lates, with deep grooves between 

 them. 



