4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 



ment throughout this entire study, and also to Dr. Ernest N. Cory, 

 head of the Entomology Department, University of Maryland, for 

 his helpful criticisms. The assistance of the United States National 

 Museum in the loan of certain immature stages of Coleoptera for 

 study is appreciated as is also that of several specialists in the Divi- 

 sion of Insect Identification, Bureau of Entomology and Plant 

 Quarantine, for their help in the identification of certain species. 



I. GENERAL DISCUSSION OF THE MUSCULATURE 



Among the orthopteroid insects there is apparently, with minor 

 variations, a general plan of muscle arrangement. The American 

 cockroach, Periplaneta americana L., is selected as a representative 

 of Orthoptera exhibiting the generalized plan of musculature. The 

 muscles included in this work are numbered for convenience of study 

 and their homologies in other species and orders are considered. 



The muscles are considered as occurring in definite pairs unless 

 indicated as otherwise. The muscles in the dorsal region of the head 

 inserted on the stomodaeum posterior to the paired nerve (frontal 

 connective) that connects the frontal ganglion with the brain are con- 

 sidered as belonging properly to the f rons ; those muscles that are 

 anterior to this nerve belong to the clypeal region proper. 



1. Compressor muscle of the labrum (fig. i). — An asymmetrical 

 muscle arising in the posterior region of the dorsal wall of the labrum; 

 inserted along the lateral margin of the ventral wall of the labrum. 



2. Dilator muscle group of the labrum (figs, i, 2). — A transverse 

 band of fibers extending across the ventral wall of the labrum. 



3. Ventral (posterior) muscle of the labrum (fig. 2). — Arises in 

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

 antennal rim and is inserted laterally at the base of the labrum on the 

 torma. 



4. Dorsal (anterior) muscle of the labrum (fig. 2). — Arises near 

 the center in the posterior region of the frons and is inserted me- 

 dially on the posterior dorsal margin of the labrum. 



5. 6, and 7. Dorsal dilator muscles of the cibarium (figs, i, 2).' — 

 Arise on the clypeal region slightly laterally and, with the exception 

 of muscle y, are inserted in the anterior region of the dorsal wall of 

 the cibarium. Muscle 7 is inserted on the dorsal wall of the cibarium, 

 midregion, between the transverse muscles, 12, of this area. 



8. Dorsal dilator muscle of the cibarium (figs, i, lA, 2). — Arises 

 centrally in the anterior clypeal region ; it surrounds muscle 4 (fig. lA) 

 and extends ventrad to be inserted in the anterior region of the dorsal 

 surface of the cibarium. This muscle was found only in Periplaneta 

 americana L. 



