FARTS OF A MUSCLE. 195 



§ 575. Subdivisions. — As has Ibeen well stated by Humphrey 

 (E, 110), the longitudinal subdivision of a muscle may be either 

 vertical or horizontal. For the sake of distinctness, we shall call 

 the subdivisions of the former kind dimsiones, and those of the lat- 

 ter lamincB. For example, as has been remarked by the senior 

 author (20, 306), the ' ' M. ectopectoralis (Fig. 72) tends to separate 

 into superimposed laminae, while the entopectoralis tends to form 

 fasciculi." In the former the " cleavage" is horizontal, in the lat- 

 ter vertical. 



§ 576. Peirts of a Muscle. — The essential and usually largest 

 portion of a muscle is the mass of muscular fibers ; this is called its 

 body or belly. 



Sometimes one — rarely if ever both — of the ends of a muscle is 

 attached to bone directly or rather to its periosteum. This is the 

 case with the humeral end of the M. hracMalis (Fig. 74, § 692), and 

 the M. entotriceps, div. intermedia (Fig. 75, § 686). 



More often, however, there intervenes between the muscular por- 

 tion and the bone a cord or sheet of white inelastic fibrous tissue, 

 constituting the tendon. The attachment is then said to be tendi- 

 nous, while in the former case it was muscular. 



Tendons may be so short as to be hardly distinguishable, like 

 the coracoid tendon of the J/", coracoideus (§ 668), or they may be 

 longer than the muscular portion, like the humeral tendon of the 

 same muscle (Fig. 75). 



Sometimes, especially with thin flat muscles like the laminse of 

 the M. ectopectoralis (Fig. 72), the tendinous sheet may be so short 

 as to be practically absent. 



§ 577. Attachment Lines and Areas. — Muscular attachments 

 usually, and tendinous attachments sometimes, cover considerable 

 areas (braohialis. Fig. 68) ; in other cases the attachment is along 

 lines {entopectoralis, dimsio caudalis, Fig. 69). 



§ 578. Origin and Insertion. — Of the two attachments of a mus- 

 cle, one is called origin and the other insertion. Usually, but not 

 always, the origin is from the more fixed part of the body, and the 

 insertion is upon the more movable part. 



§ 579. Choice of Origin and Insertion. — With the membral 

 muscles, one attachment is generally nearer the soma (§ 54) or the 

 proximal end of the limb, and this attachment is always called the 

 origin. Thus the scapular attachments of the MM. biceps (Fig. 75) 

 and subscapularis (Fig. 73) are the origins of those muscles ; so 



