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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



out, only the crosswise dorsal and ventral muscles are literally trans- 

 verse in position. Again, the body muscles are sometimes classed 

 as dorsal, ventral, and lateral muscles, the dorsals and ventrals com- 

 prising longitudinal, oblique, and transverse fibers, and the laterals 

 including dorsoventral and oblique fibers. This classification is evi- 

 dently the most nearly consistent one that can be devised, and it has 

 the added merit of being in conformity with the embryonic develop- 

 ment of the muscles. Unfortunately, however, in naming the secon- 

 dary muscle groups or individual muscles according to it. the plan 

 brings out such terms as " median longitudinal dorsal muscles," " ex- 

 ternal median longitudinal dorsal muscles," or " second internal median 



Fig. 13. — Diagrams of the nK)rc simple types of segmental musculature. 



A, simple condition of musculature in right half of a segment, with dorsal 

 (d) and ventral (v) fibers attached intersegmentally, external laterals (le) 

 intrasegmentally, and internal laterals (li) on intersegmental folds. 



B, upper ends of internal lateral muscles (/;) migrated posteriorly, separating 

 a paratergal muscle band (p) from the rest of the dorsal muscles {d). 



C, cross section of segment, showing relations of principal groups of muscles. 

 dl, lateral dorsal muscles; dm, median dorsals; le, external laterals; //, internal 

 laterals; p, paratergal muscle; td, dorsal transverse muscles; tv, ventral trans- 

 verse muscles ; ?', ventrals. 



longitudinal dorsal muscle." Still more unwieldy do such terms 1)e- 

 come when put into Latin form. 



It is evident that strict anatomical and nomenclatural consistency in 

 dealing with the body musculature leads to impractical results. The 

 writer, therefore, has adopted a classification and nomenclature that 

 recognizes the anatomical arrangement of the muscles, but which, 

 in order to shorten the names, errs somewhat on the side of specificity 

 in terminology. Five principal groups of muscles are distinguished 

 and designated as follows: I. dorsal muscles (fig. 13 A, d), the 

 fibers of which are typically longitudinal and primarily intersegmental 

 in their attachments. II. ventral muscles (v), resembling the 

 dorsals in that their fibers are typically longitudinal and attached 

 primarily on the intersegmental lines. III. lateral muscles (/), 



