ii6 



SMITHSONIAN MISCF.LLANEOrS COLLECTIONS VOL. 8l 



The Dilator Muscles of tJic Stomodeuni.—Th\rttQ.n paired sets of 

 muscle fibers and one median unpaired muscle arising on the skeletal 

 parts of the head or thorax are inserted on the stomodeal walls in 

 Dissosteira (figs. 41, 43, 44). These muscles may be classed as dor- 

 sal, lateral, and ventral according to their insertions, though because 

 of the downward flexure of the pharynx, the first " dorsal " and 

 " ventral " muscles are anterior and posterior. The dilator muscles 

 of the stomodeum, sometimes called also suspensory muscles, enumer- 

 ated from 55 to 46 inclusive, are as follows : 



Fig. 44.— Dilator muscles of the buccal region, pharynx, and crop of 

 Dissosteira Carolina. 



CocCon, circumoesophageal connective: Cr, crop; Mth. mouth; Tut. tentorium. 



55. — First anterior dilators of the buccal cavity (figs. 41, 44). — 

 A pair of fan-shaped muscles arising on inner wall of clypeus (fig. 

 37 B), the fibers spreading to their insertion on anterior wall of buccal 

 cavity (fig. 44) mostly distal to oral aperture. 



^4. — Second anterior dilators of the buccal cavity (figs. 41, 44). — 

 A pair of fan-shaped muscles similar to j?, arising on clypeus near 

 epistomal ridge (fig. 3/ B) ; inserted laterad of jj and mostly proxi- 

 mal to oral aperture. 



J5. — First dorsal dilators of the pharynx (figs. 41, 44). — A pair of 

 slender muscles arising on frontal area of head wall, each attached 

 between labral retractors of same side (fig. 38 D) ; inserted on anterior 

 wall of pharynx. 



