Physiology of the Muscles. 491 



of the auditory nerve. These currents all tend to a common center in 

 the spinal cord and brain, and are returned thence along the efferent 

 nerves to the muscles, stimulating them to contraction. The greater 

 part of the energy of the nervous current is consumed in the work of 

 muscular contraction that is, disappearing as nervous energy it reap- 

 pears as work, and so passes on out of the system back into the environ- 

 ment, which furnished it in the first place. 



It will be seen also that tetanus of a muscle, or a continuous strain of 

 the fibres, causes them to give off an electrical current. Such action is 

 also accompanied by heat. The physiological change in the muscle 

 when contracted consists in the elimination from its tissue of some of 

 the elements, especially some of the carbon composing it, and its union 

 with oxygen contained in the blood, forming thereby carbonic acid, 

 which is carried off through the lungs. A part of the heat liberated in 

 the destruction of the muscle tissue is immediately turned into electric- 

 ity, and may be conveyed as such by proper appliances and stored in a 

 Leyden jar. All muscular action produces heat and without doubt elec- 

 tricity, too. 



The number of muscles in the human body is variously reck- 

 oned as low as 368 and as high as 400. The greater number are 

 in pairs. A few are azygos 1 , as the heart, diaphragm, several of the 

 sphincters 2 , &c. They are of various shapes : long, broad and short. 

 They are said to be Simple when the fibres all run parallel with each 

 other in one body or " belly, "as 8 sartorius, *pronator-quadratus, &c ; 

 Compound, when with one body they are connected with their attach- 

 ment or insertion by two or more tendons, or when there are several 

 connected bellies and several tendons, as 5 biceps-flexor-cubiti, 6 sacro-lum- 

 halis, &c. ; Radiated, when the fibres diverge from a common center 

 like rays, as the 7 diaphragm, 8 iliacus, 9 temporal, &c ; Pennated or 

 Pinniform, when their fibres are arranged in two rows which are united 

 to a tendon in a median line, at an angle, like the feather fibres of a 

 quill to its central stem; as the palmaris-longus ; Semi-penniform, 

 when the fibres are oblique but joined on one side of the tendon only, 

 like one-half of a split quill. Hollow muscles are such as the heart, in- 

 testines, urinary bladder, &c. They are likewise distinguished as vol- 

 untary, and striped or striated, and involuntary smooth muscles. The 

 former are those which ordinarily are, or may come under control of 



1 Un-yoked, hence not paired. 



2 Muscles in the form of a rin^ for closing an orifice like the mouth, &c. 

 8 Tailors' muscle, used in raising the leg to cross it. 



4 In the fore-arm. It rolls the fore-arm and hand inwards. 

 6 Bends the fore-arm upon the arm. 



6 In lower part of the back ; straightens the backbone backward. 



7 Partition across the body cavity. 



8 Connects lower part of the trunk with upper part of thigh ; holds the trunk from fall- 

 ing backward. 



9 On side of head ; raises lower jaw. 



10 A long muscle in the arm for bending the hand. 



