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 find 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 belly; while the opposite 
attachment is the faz/ or insertion. These extremities are usually 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 parallel 
to each other, and are either 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 obliquely, those on the same side being 
nearly parallel, the muscle is said to be penniform (musculi pennati); sem- 
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, Xe. 
_ 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 
trochlez.. The patella is an illustration of this ossification of tendon, as 
also the sesamoid bones found under various circumstances. ‘T'endons are 
frequently confined to a motion in one direction by passing through sheaths, 
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