MYOLOGY. 45 



antagonists, or muscles whose action is in a directly contrary direction ; the 

 equilibrium being maintained by the influence of the nerves, the brain, and 

 the spinal marrow. 



Considering a muscle in itself, we lind that at the more fixed place of its 

 attachment it is usually thinner than elsewhere ; this portion is called the 

 head or origin ; the middle and thicker part is the helly ; while the opposite 

 attachment is the tail or insertion. These extremities are iLsually tendinous, 

 either entirely or partly. Their forms vary with the motion to be effected. 

 Radiated muscles are those in which the fibres converge to a common point 

 from a wide base, as in the diaphragm. Sphincter muscles are circular or 

 annular, inclosing some cavity to be shut by their contraction, as in the 

 eyelids, the mouth, and the anus. Broad muscles are thin and wide-spread, 

 surrounding large cavities, as in some of the abdominal muscles. They 

 usually arise by slips or points from neighboring muscles, and are inserted 

 by a broad skin-like tendon. In longitudinal muscles the fibres run jiarallel 

 to each other, and are eitlier simple or compound. They are simple when 

 they arise by a single head and are inserted into one point, and compound 

 when there is a plurality of either heads or insertions, or of both. Some 

 arise by numerous digitations or dentations, with one belly ; others have 

 several bellies. When there is a long tendon in the centre, to which the 

 fibres from opposite sides converge obliqueh', those on the same side being 

 nearly parallel, the muscle is said to be penniform (musculi pennati); semi- 

 pennati, when the fibres are on one side only. 



Muscles, in respect to their antagonism, bear different names, according 

 to the precise nature of the motions effected by them. Thus we have flexors 

 and extensors, sphincters, elevators and depressors, protractors and retract- 

 ors, &c. Their nomenclature also varies with their position, direction, shape, 

 size, combination, origin, attachment, &c. 



Muscles are assisted in their operation by tendons, usually placed at the 

 insertion, but sometimes at both origin and insertion. They may exist at 

 either end or at both, and again may not occur at all. Tendons may pre- 

 sent themselves under two shapes : one like a cord, varying from cylindrical 

 to paraboloid; the other is spread out into a membrane, and resembles an 

 aponeurosis. They are readily recognisable by their white and shining 

 appearance, possessing no elasticity ; they are lacerated sooner than they 

 can be stretched. They are composed of desmoid tissue, the fibres of 

 which are united by a compact cellular substance in small quantities. The 

 fibres are longitudinal, and may readily be separated by maceration or slight 

 boiling. In ordinary health no red blood penetrates the tendons; in inflam- 

 mation, however, their capillaries may become so much enlarged as to 

 admit red globules; no nerves have ever been traced into them. They 

 are more soluble in boiling water than the ligaments. They have a great 

 affinity for phosphate of lime, and hence they are frequently found hardened 

 by the development of bony matter, especially where they run over long 

 trochlete. The patella is an illustration of this ossification of tendon, as 

 also the sesamoid bones found under various circumstances. Tendons are 

 frequently confined to a motion in one direction by passing through sheaths, 



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