450 



ANNUAL REPOET SMITHSONIAN INSTITUTION, 19 31 



The true buccal cavity of the insect is the anterior part of the 

 stomodeum lying immediately within the mouth (fig. 4, BuC). It is 

 to be identified by the attachments of its dorsal dilator muscles 

 {dlhuc) on the head wall, the origins of these muscles being always 

 on the lower part of the face known as the clypeus {Glp). Ordi- 

 narily the buccal cavity is small, but in some insects it is greatly 

 enlarged to form a sucking pump. 



Vx dlppKy Cv T-^ 



FiODEE 4. — Diagrammatic median vertical section of an insect's head 

 Ao, aorta ; APhy, anterior pharynx ; Br, brain ; BuC, buccal cavity ; 

 Glp, clypeus ; cplr, compressor muscles of labrum ; Cv, necli ; dlaphy, 

 dilator muscles of anterior pharynx ; dlhuc, dilators of buccal 

 cavity ; dlpphy, dilators of posterior pharynx ; Ephy, epipharynx ; 

 Fr, frons ; FrOno, frontal ganglion ; Hphy, hypopharynx ; Lm, 

 labrum; mlra, anterior labral muscle; mlrp, posterior labral mus- 

 cle ; Mt, mentum ; Mth, mouth ; Oe, oesophagus ; Pmt, prementum ; 

 PPhy, posterior pharynx ; PrC, preoral cavity ; SID, salivary duct ; 

 BIO, opening of salivary duct ; 8mt, submcntum ; SoeQng, sub- 

 oesophageal ganglion ; Ti, tergum of prothorax ; Tnt, tentorium ; 

 Vm, vertex. 



Following the buccal cavity is the pharynx (fig. 4, APhy), a spec- 

 ialized part of the stomodeum usually ending between the nerve con- 

 nectives that unite the brain (Br) with the suboesophageal ganglion 

 {SoeGng). The dilator muscles of the pharynx arise on the head 

 wall above the region of the clypeus and on the tentorium {Tnt). 

 In certain insects, particularly in Orthoptera and Coleoptera, the 

 pharynx extends beyond the nerve connectives, and its two parts, 

 separated by the nerve ring, are then distinguished as the anterior 

 pharynx {APhy) and the posterior phai^nx {PPhy). In some suck- 



