MIS. i, i : 



into ( 1 ) a thin dim disc whose edges appear 

 to adhere to the sarcolemma, (2) a clear sjtace, 

 (:t) a broad dim disc, (4) a clear space like 2, (5) 

 another disc like I, \c. 



Nerve fibres pierce the sarcolemma, and end 

 u|in the contractile substance (see NKRVors 

 S\-IIM). No blood -vessels penetrate the car- 

 colcnima; they merely lie in tin- intervals be- 

 tweeu the libres. Through the medium (if tendon 

 nr aitoneiirosis the muscular fibres are attached 

 to the parts which thev are intended to move. 

 Aggregated in parallel series, of greater or 

 -i/.e, and associated with nerves, vessels, 

 tendinous structures, &c., they form the various 

 muscles, which are for the most part 

 solid and elongated, but are sometimes 

 expanded ( as in the diaphragm ) into 

 a membranous shape. In the human 

 subject voluntary muscles are red, 

 and although pale fibres are scattered 

 through many of them, still nothing 

 is ever seen to correspond with what 

 may be found in the muscles of the 

 rabbit. The colour is due to a sub- 

 stance closely akin to the blood-pig- 

 ment. Each muscle has a middle portion 

 or lull ii and two extremities which are 

 attached. When the belly contracts it 

 acts in a straight line, and drags equally 

 on both extremities ; hut, as one is more 

 fixed than the other, the force is s|tent 

 in bringing the movable attachment 

 nearer to the fixed one, and thus the 

 fixed end is named the origin, the mov- 

 able end the insertion. Muscles are 

 usually grouped around joints, and 

 attached to bone. 



The involuntary or unstriped muscular 

 -_._. tissue most commonly occurs in the 

 Muscular shape of flattened bands of considerable 

 Fibre-cells length, but of a width not exceeding 

 fr m f *{," ""a* 1 ' 1 or !">Vith of an inch. Their sub- 

 cpatofthe stance presents line longitudinal mark- 



ftdtnll In . ,, 



ings, and each cell possesses an elon- 

 gated nucleus, towards each end of 

 which a few fine granules arc found. 

 Kolliker has shown that every one of 

 these liands or fibres is either a single 

 elongated cell (a fibre-cell ) or is a fasci- 



work and c ."' us of 8UC '' ce " N < see <-'KM-)- These 

 lmigitu.il- fibres have not usually fixed point* of 

 mi! tlurilla- attachment like the striated fibres, but 

 ; 6, cell form continuous investments around 

 , , cavities within the body, such as the 

 iaolatlon. intestinal canal, the blood-vessels ; or 

 are dispersed through the suliMance of 

 tissues, such as the skin, to which they impart a 

 contractile proper; \ 



t'linliiH- muscle, although involuntary, differs in 

 a remarkable manner from the fibres just described. 

 It consists of quadrangular cells, which are often 

 branched at their ends. Kach cell has a clear oval 

 nucleus near its centre, and the cells present 

 transverse stria- not sit distinct ami less regular 

 than those of voluntary muscle. Hitherto the-i- 

 cardiac fibres have not been shown to possess a 

 sarcoleinma. 



The chemical com|>o-itioii of ordinary <tr volun- 

 tary muscle is descrilied at KI.KSII. The fihrilhr. or 

 the sarcous elements of which they are composed, 

 consist of a sultstance termed Syntonin (q.v. ), 

 which closely roemliles the lihrine or coagulating 

 constituent of the blood ; and the same syntonin 

 is also the main constituent of the unstri|x-d 

 muscles, or at all events of their fibre-cells. Like 

 the blood-fibrino. it exists in a fluid form in the 

 living tissue, and only coagulates or solidifies after 

 d-.tth. 



Fig. 5. 



Small In- 

 testine (af- 

 terQuain): 

 a, complete 

 c- 11 show- 

 ing nucleus. 

 Intranuc- 

 lear 



Fig 6. Muscular 

 Kil.rc-c. 11* from Hu- 

 man Artery (after 

 Kolliker): 



n, nnrlf in : '. cell tinted 

 with aortic acid. 



Muscles vary extremely in their form. In the 

 limbs they are usually of considerable k-ngtli, 

 surrounding the (tones and 

 forming an important protec- 

 tion to the joints ; while in 

 the trunk they arc flattened 

 and broad, and contribute 

 very essentially to form the 

 walls of the cavities which 

 they enclose. Muscles derive 

 their names variously i 1 ) 

 from their situation as the 

 temporal, |K-ctorals, glut.rals ; 

 or (2) from their direction 

 as the rectus, obliquus. &c.. 

 of which there may ite several 

 pairs as, for example, rectus 

 lemons, rectus capilis ; or (3) 

 from their uses as the mas- 

 se ter, the various flexors, ex- 

 tensors ; or ( 4 ) from their 

 shape as the deltoid, trape- 

 zius, rhomboid ; or (5) from 

 the number of their divisions 



as the biceps and triceps -. or (fi) from their points 

 of attachment as the stemo-cleido-mastoid, the 

 sterno-thyroid. 



The skeleton, which may be 

 termed the locomotive framework, 

 may lie regarded as a series of 

 levers, of which the fulcrum is, for 

 the most part, in a joint viz. at 

 one extremity of a bone the re- 

 sistance ( or weight ) at the further 

 end, and the force (or muscle) in 

 the intermediate portion. In most 

 cases, in order to preserve the neces- 

 sary form of the Itody, muscles are 

 applied at a great mechanical dis- 

 advantage as regards the exercise of 

 their power; that is to say, u much 

 larger force is emploved than would 

 suffice, if differently applied, to 

 overcome the resistance. The two 

 main sources of this disadvantage Fig. 7. Muscular 

 lie in the obliquity of the inser- Fibres from the 

 tion, and consequent ly of the action Heart. 

 of most muscles, and in the muscles 

 lieing usually inserted very near the fulcrum. The 

 first of these" disadvantages U in many cases dimin- 

 ished by the enlargements of the IHUICS at the 

 joints. See fig. 8, A. 

 The tendons (') of the 

 muscles (m) situated 

 altove the joint are usu- 

 ally inserted Immediately 

 below the bony enlarge- 

 mi-lit, and thus reach the 

 bone that is to ! moved 

 (o) in a direction some- 

 what approaching the per- Fig. 8. 

 pendicular. If this en 



largenwnt did not exist (as in fig. 8, B), the con- 

 traction of the muscle, instead of causing the 

 lower lione to turn upon the upper one with 

 comparatively little loss of power, would do little 

 more than cause the two ends of the IHM- to 

 press upon each other. The sirond mechanical 

 disadvantage is comjtensated for by gain in the 

 extent and velocity of movement, and by the 

 avoidance of the great inconvenience of having 

 the muscles extended ill straight lines between 

 the ends of jointed continuous levers. Thus, the 

 liones of the forearm (fig. 0, b, c) are bent upon 

 the Ixuie of the arm ()by the biceps muscle (</). 

 which arises close to the head of the latter, and is 

 inserted ate, at a short distance from the elliow- 

 joint, which acts as the fulcrum of the lever (c). 



1 



