STRUCTURE OF ONVCIIOPHORAN HEAD — BUTT 



49 



7. Lateral dilators of the oral lobes; large flat sheets of muscles 

 originating on the body wall near the bases of the antennae ; inserted 

 in the large lobes adjoining the median dorsal lobe (fig. 3 A, Idm). 



8. Lateral sphincter muscles of the oral lobes. These are large 

 sheets originating on the anterior head wall; inserted ventrally and 



vphd— 



FiG. 3. — Dissections of the oral lobes, and the salivary pump. 



A, dorsal dissection with inner wall of preoral cavity removed showing salivary 

 pump. B, salivary pump with ventral muscle sheet removed to expose the entire 

 salivary pump. C, same dissection with the median salivary duct removed. 



iB, outer lobe of salivary pump; 2B, inner lobe of salivary pump; Dl, dorsal 

 lobe ; Sd, salivary duct ; Icsp, lateral compressors of salivary pump ; Idm, lateral 

 dilators of the oral lobes ; Icxsp, lateral extensors of the salivary pump ; Ispm, 

 lateral sphincter of the oral lobes ; mcsp, median compressors of salivary pump ; 

 mexp, median extensors of salivary pump; vld, ventral longitudinal dilators of 

 the oral lobes; vphd, ventral dilators of the oesophagus. 



posteriorly in the oral lobes near the insertions of the ventral longi- 

 tudinal dilators of the oral lobes (fig. 3 A, Ispm). 



These muscles lie exterior to the lateral dilators of the dorsal lobes 

 and, when contracted, pull the ventral oral lobes together, thus helping 

 to close the mouth. 



Other small sheets of muscles not shown in the figures for this 

 paper lie near the body wall and are inserted in the lobes, apparently 

 just a few fibers to each lobe. Some of these lie underneath the lateral 

 sphincter muscles and are inserted in the lateral oral lobes much as 



