NO, 7 MUSCULATURE OF COLEOPTERA — DORSEY 9 



extends slightly diagonally and anteriorly to become inserted on the 

 dorsal wall of the cibarium, anterior region ; this is a compressor 

 muscle of this region that may be homologous with the compressor 

 muscles of the anterior region of the cibarium, Jj (fig. 2), in the cock- 

 roach. The two modified sclerites, bars Y (fig. 14), support the sides 

 of the cibarium and stomodaeum ; they are united by a continuously 

 sclerotized area that strengthens the ventral wall of the stomodaeum. 

 Muscle J-/ (fig. 15) is inserted laterally on the distal end of the bar 

 Y; this muscle extends laterally and anteriorly to its point of origin 

 in the posterior region of the frons adjacent to the inner margin of 

 the compound eye. The dorsal dilator muscle of the pharynx, 11 

 (figs. 14, 15), consists of a compact group of fibers and probably is 

 a homolog of muscle 11 in orthopteroid forms. The ventral dilator 

 muscle of the pharynx, jo (fig. 14), is especially large and powerful; 

 it arises on a sclerotized central projection from the anterior (dorsal) 

 surface of the tentorial bridge by means of a tendon ; it is inserted 

 medially on the ventral surface of the continuous sclerotized area 

 that supports the stomodaeum. This is a dilator muscle of the 

 stomodaeum. It was thought on first examination that muscle 55 

 (figs. 14, 15) was homologous with the muscle of hypopharyngeal 

 bar Y, 10 (fig. i), in Periplaneta; this is not the case because the 

 small frontal ganglion with its connectives lies posterior to this muscle, 

 the function of which is not certain. In the honeybee, Apis mellifera 

 L., there is a muscle which undoubtedly is homologous with the 

 muscle of the hypopharyngeal bar Y, 10, found in Periplaneta;^ it 

 consists, of an anterior and a posterior branch inserted on the dis- 

 tal end of bar Y, and is posterior to the frontal connective nerve. 



II. MUSCLE ARRANGEMENT IN COLEOPTERA 



The muscles of adult and immature Coleoptera included in this 

 work are numbered as in Periplaneta and are considered to be 

 homologous with those of the same designation in the orthopteroid 

 forms unless indicated as being otherwise. 



Certain muscles appear generally and consistently throughout the 

 adult and immature stages in the order, though there are specialized 

 muscles found in certain species and also generalized muscles that 

 are greatly modified in size, shape, origin, and insertion. By con- 

 sidering the muscles of each superfamily separately it is easier to 

 interpret homologies and the probable function of the various muscles. 



