993 



MUSCLE. 



MUSK. 



991 



of the third or fourth month that their elementary constituents can 

 be made out. 



All the muscles receive large arteries and veins from the trunks 

 passing near to them, whose branches run in the cellular interspaces 

 between the fasciculi, and form at last an irregular network among the 

 fibres. They receive also a large supply of nerves, probably more 

 than any other organs in the body. Nearly one-half of the brain and 

 spinal chord is for the supply of nerves through which the will may 

 act upon the voluntary muscles, or through which their motions may 

 be excited by other stimuli. The involuntary muscles are chiefly sup- 

 plied from the ganglionic or sympathetic system of nerves. [NERVOUS 

 SYSTEM.] 



The colour of the muscles is dependent partly on the blood which 

 they contain, but chiefly on a peculiar colouring matter, very similar 

 to that of the blood, which is fixed in their tissue. Their colour is 

 distinctly though remotely connected with the quantity and condition 

 of red blood in the system, and its depth is one of the best signs of 

 robustness and full health. Thus, in all quadrupeds and birds the 

 muscles are more or less red, and the colour is deepest in the parts 

 which are most actively employed, but pale and scarcely perceptible in 

 those which have not been frequently exerted, and also in those 

 animals which, by being closely stalled and stabled, are killed in a 

 condition of great debility ; hence the difference between red and 

 white meats. In Amphibia, which have less red blood than Mammalia 

 and Birds, the muscles are usually pale. In Fish, which have still less, 

 they are, with the exception of the heart and those which move the 

 fins and are particularly exerted, quite white. There are however 

 some exceptions, as the salmon and tunny. In animals of a still 

 lower order, the muscles, though still preserving the same structure, 

 are all quite white. 



The peculiar vital power of the muscular tissue is its contractility ; 

 that IB, the power which its fibres possess, when stimulated by the 

 will or other means, of shortening themselves, and thus approximating 

 the points to which their extremities are attached. When muscles 

 contract they become shorter, harder, and thicker ; but their actual 

 size remains the same, for what they lose in length they exactly gain 

 in breadth and thickness. The fasciculi are also wrinkled or thrown into 

 undulated lines, which are most visible when the contraction is least 

 powerful and rather trembling, and the fibres vibrate so as to produce 

 a distinct sound. The more powerful the contraction the more rapid 

 are the vibrations of the muscular fibres ; the higher the note which 

 they produce, and the greater the difficulty of perceiving them with 

 the eye. The simplest method of observing the sound of muscular 

 contraction is that which Dr. Wollaston pointed out (' Croonian 

 Lecture,' 1809) : when the tip of the thumb, or of one of the fingers, 

 is put into the external ear, while some of the muscles of the former 

 are in a state of contraction, a sound is heard like that of carriages 

 running rapidly over a distant stone pavement. This sound is not 

 heard when the same degree of pressure is applied to the same part by 

 any other means than those in which muscular contraction is concerned. 

 By rubbing a piece of stick over the notched edge of a board so as to pro- 

 duce a similar sound, and counting the number of notches whose edges 

 were struck in a given time, Dr. Wollaston concluded that the number 

 of vibrations of a contracted muscle is between 20 and 30 in a second. 



The relaxation of a muscle presents phenomena exactly the con- 

 verse of those of its contraction. The power by which the voluntary 

 muscles are lengthened after having contracted is generally the exten- 

 sion to which, when they cease to act, they are subjected by some 

 other muscles (their antagonists), whose action is the opposite of their 

 own. The hollow involuntary muscles are usually extended after 

 contraction by the accumulation of fluids or other substances forced 

 into their cavities by some external power. It may be yet a question 

 whether muscles have a vital and independent power of dilatation as 

 well as of contraction ; but on the whole the evidence is in favour of 

 their possessing such a power, for the heart will contract and dilate 

 when empty, if external stimuli are applied, and the hearts of reptiles 

 when hung in the air will sometimes go on contracting and dilating 

 till they are nearly dry and stiff. Were there no vital power of dilata- 

 tion, it a difficult to conceive how the heart or any other muscle when 

 separated from the body should, after having once contracted, be 

 dilated so as to be able to contract again. 



When muscles shorten however it is not always by an exercise of 

 their peculiar vital contractility, but often by their elasticity, by 

 which, like all the other tissues, they are always maintained in a 

 certain degree of tension. Thus when a muscle is divided, its ends 

 retract as well after death, or when its nerves are cut, as during life 

 and health. It is by this power that muscles, after having been much 

 extended, generally return to their natural size ; thus, when a muscle 

 on one side of the joint of any limb shortens, it is evident that its 

 antagonist on the opposite side must be lengthened in the same pro- 

 portion, and when the contracting muscle ceases to act the elasticity 

 of the extended one (increased by the tension to which it has been 

 subjected) will be alone sufficient in most eases to restore the limb to 

 its position of rest. 



The actual power with which a muscle contracts is in direct propor- 

 tion to the number of its fibres, and inversely as their length. Hence, 

 in all the muscles in which great strength is required, as in the chief 

 muscles of the shoulder and hip, the fibres do not run straight from 



HAT. BIST. DIV. VOL. III. 



the general point of origin to that of insertion, but the whole mass 

 of the muscle is divided into a number of small portions, in which a 

 multitude of short fibres are attached to separate points within the 

 muscle, so that they may act separately, or, when great exertion is 

 necessary, altogether, and with far greater power than a smaller 

 number of long straight fibres could. The strength of a muscle is 

 very commonly increased by its fibres not running parallel to the line 

 in which the muscle has to draw the part to which it is attached, 

 but with various degrees of obliquity to that line. Thus in many 

 muscles the fibres and fasciculi are attached obliquely to one or both 

 sides of a tendon, as the fibres of a feather are attached to its shaft ; 

 by which arrangement, though each muscular fibre contracts in its 

 own direction, the general result of their contraction and the direction 

 in which the resistance will act upon them forms an oblique angle 

 with then- direction, and much of the danger of their being ruptured 

 is removed. There are indeed but few instances of rectilineal muscles 

 in the body ; in nearly all, the fibres are placed more or less obliquely 

 to the line in which they have to draw the part to which they are 

 attached ; a plan by which, though individually they lose in active 

 power, they gain in resistance, and by which a far greater number 

 may in the same space be brought to bear upon a given point. 



An almost infinite variety of arrangement is found in the muscular 

 fibres adapted to the especial purpose which each muscle has to fulfil, 

 whether it be chiefly strength of action, or rapidity or extent of 

 motion ; and all are guided by the nicest mechanical rules. Wherever 

 strength is more necessary than a wide extent of motion, the fibres 

 are increased in number and placed obliquely to the direction of the 

 resistance ; wherever extent of motion is more needed than strength, 

 the fibres are long, and run almost straight from one point to the 

 other, so as to give the full benefit of their contraction ; where 

 velocity is required, they are placed at a part of a lever close by the 

 centre of motion, the resistance being placed on a part more distant 

 from the centre. In general, the absolute power exerted by a muscle 

 in contracting is much less than its efficient power, a great part of its 

 force being lost in its being inserted obliquely on the lever which it 

 has to move, or in the distance of the resistance from the centre of 

 motion, or in the resistance which other muscles and the adjacent 

 tissues, which have to be extended, present, &c. But it is constantly 

 found that where power is lost, a corresponding gain of velocity or 

 extent of motion, or of convenience and compactness of form, and 

 readiness of action, is obtained. 



(On the subject of the Structure of Muscle and its Functions, the 

 student will find information in the following works : Carpenter, 

 ' Principles of Human Physiology ; ' Todd and Bowman, ' Physiologi- 

 cal Anatomy ; ' Valentin, ' Textbook of Physiology ; ' Kirkes, ' Hand- 

 book of Physiology;' Kb'lliker, 'Manual of Human Histology;' 

 Wagner, ' Manual of Physiology.') 



MUSCLE, or MUSSEL. [MYTILIDA] 



MUSCULAR TISSUE. [MUSCLE.] 



MUSHROOM. [AGARICUS; FUNGI.] 



MUSK. This substance is an extremely odorous secretion, lodged 

 in a bag which is attached and peculiar to the abdomen of the male 

 Musk-Deer (Moschus Afoschiferus). [MosCHiD*.] The elevated regions 

 frequented by the creature, its timidity, and speed in flight, render it 

 very difficult to obtain the substance, while the high price borne by it 

 offers great inducements to substitute other articles for that which is 

 genuine. The musk-bag varies much in form, colour, size, and quality, 

 circumstances which suggest the belief that it is procured either from 

 two or more species of musk-animals, or that it has been obtained at 

 different periods of the year, or from very differently-aged animals. In 

 the very young animal the bag is quite empty, while in the old and 

 feeble the musk is in small quantity and of inferior strength. It is said 

 to be secreted in greatest abundance during the rutting season, and to 

 have then its sensible qualities most developed. The secretion has a 

 much stronger odour in the animal which inhabits Tibet and China than 

 in that which frequents the more northern districts of Siberia. In the 

 fresh state the musk has an extract-like consistence, and a reddish- 

 brown colour, with an odour so powerful that the huntsmen can scarcely 

 endure it. This odour diminishes by drying, and the musk acquires 

 a friable granular state, and a dark brownish colour. In Siberia the 

 chase occurs in spring and summer. In Tibet the pursuit is restricted 

 by the government to certain periods, and the bags which are obtained 

 are stamped with the royal signet. In commerce two and occasionally 

 three varieties of Musk are met with. 



1. The Tonquin, or Tibet Musk, received through the East India 

 Company, occurs in small oblong rectangular boxes, lined with lead, 

 and covered with paper or silk. Each bag, or pod, as it is termed, is 

 wrapped in thin blue or red paper, on which are marked some Chinese 

 characters. Sometimes the bags are enveloped in a deep yellow 

 brownish nearly transparent paper, which becomes brittle by time. 

 The most distinctive mark of this sort of musk is, that it is slightly 

 flattened, nearly round, and very rarely pear-shaped. The yellow or 

 yellowish-brown hairs, chiefly at the sides, are often cut, while those 

 which remain in the centre are darker coloured, finer, and less bristly. 

 Generally the hairs converge or point towards a small natural opening. 

 The pods are mostly about two inches and a half long and one inch 

 and three-quarters broad. The weight of different specimens varies 

 considerably, some being merely 3 drachms 30 grains, others 9 drachms 



3 s 



