374 



MUSCULAR ACTION 



of the relations of the muscles and functional groups to their nerve- 

 and blood-supply should likewise be thoroughly in mind before the study 

 of this chapter is begun. 



Fio. 225 



Cilio-epithelio-muscular filaments of the parasite Sagastia. At the bottom of each cell one 

 sees the part most like the smooth muscle-fiber of man. (Dubois.) 



Fio 226 



ex 



The evolution of muscle: o, epithelio-muscular cell; 6, a subepithelial muscular fiber; c, a 

 longitudinal muscular fiber (from a worm); c,, transverse section of the same; e, the same in a 

 bird; d, dorso-ventral fiber (from a marine planarian); f, the same from a bird; g, branched 

 muscular fibers (from the gel of a ctenophore). (Dubois.) 



The Contractile System in Man. It is sometimes ill-appreciated how 

 nearly universal in the organism is some variety or other of contractile 

 tissue muscle. There are more than four hundred more or less inde- 

 pendent muscles classed as cross-striated or "voluntary," ranging in 

 size from the vastus externus to the stapedius and in site from the ends 



