HUMAN PHYSIOLOGY. 





. muscle* accord. 



ing to thoir locution in the gr. -, of tho body the bond 



:'ik, uinl thf i-\' 



variou* groups of muscle*. 

 1 of tho hcfvl in 



sense baa it* special group, 



vhi.-li govern its actions, ainl i.ition withsomo upocial 



muscles of tho face, ) > movement*, wonderful in 



unilior as in tho fineness of thoir gradations, which alter 



Tension of the oountonanco. The moat complex group ii 



1 with tho tongue, which in itnolf but a mass of 



u- fibre; by theso all tho changes of its form and posi- 



ho porformanoe of swallowing and speaking 



lueoil. In sizo, tho musoles of mastication excel tho 



thr-e run from th<- upi"T jaw . surface and 



head, mill uro inserted into tho lower jaw, which 



. ami from *ido to side against tho ftxod upper jaw, 



:i titrating action necessary for tho reduction of tho 



I'hn musolos oonnocted with deglutition are situated in 



the nook, and are Tory numerous ; whilst inside tho larynx or 



windpipe is a small group of muscles which make tense or 



* he vocal cords, and thus govern tho voice. 



m-'-los of the trunk aro those that are special to the 

 irnnk, ami those which connect it with tho head and with tho 

 extivmitiej. In tho back they are arranged in five layers. Some 

 of them i>a-i* upwards, to be inserted into tho back and sides 

 of the head, which they support in its erect position and turn 

 iile to side. Others, special to tho trunk, perform tho samo 

 office for the spinal column ; those run tho whole length of tho 

 spine, and are numerous and powerful. 



Several strong muscles connect tho upper extremity with tho 

 trunk. These either draw the arm upwards and backwards, or, 

 when the arm is fixed, as in climbing, draw the body upwards ; 

 iu this they are powerfully aided by the abdominal muscles, 

 presently to be noticed. The interspaces of tho ribs are filled 

 in by a number of small muscles, one set of which raises tho ribs 

 and another depresses them. Over these is a large powerful 

 muscle, which rises by fleshy digitations from nino of the ribs, 

 and is inserted into the scapula ; this strongly raises the ribs, 

 and is the most powerful of all the external respiratory muscles. 

 Assisting this are two muscles which run from tho front of tho 

 thorax to the npper part of the humerus, and also some of the 

 muscles of the neck. Acting in opposition to them are tho 

 abdominal muscles, which are arranged laterally in threo layers ; 

 in the centre are two long, straight muscles these enclose the 

 aodominal cavity, the capacity of which by their contraction 

 they diminish, and compress tho organs of the abdomen, forcing 

 upwards tho muscular floor of tho thorax, and so diminishing 

 the capacity of the chest. The only other muscular agent of 

 the respiratory function to be mentioned is the most important 

 one, tho diaphragm, which, as has been said, forms tho division 

 betwixt the cavities of the thorax and abdomen. It ia a large 

 piano of muscular fibres attached all round to the circumference 

 of the thorax, and by strong tendons to the front of the spinal 

 column. In the centre it has a tendinous portion, to support 

 the heart. By the action of this muscle tho size of the chest is 

 greatly altered ; during inspiration it pushes down tho abdo- 

 minal viscera to tho extent of two or threo inches, and thus 

 enlarges tho chest. It is, indeed, the most powerful agent for 

 this purpose. 



The muscles connecting tho trunk with tho lower extremity 

 are many in number, some of them run from the front of tho 

 spinal column, others from the pelvis to the femur. They are 

 mostly largo and powerful. It is to the great size and strength 

 of one set, that rises from tho posterior surface of the ossa 

 innominata, that man owes his ability to assume and retain tho 

 erect posture. 



In tho arm the muscles aro arranged in two groups, ono on 

 the front which bends tho arm, the other along the back which 

 extends or straightens tho arm. In tho fore-arm tho same rule 

 applies, only hero thro are additional ones to rotate tho arm, 

 and execute tho movements of tho hand. The two long flexor 

 muscles of the hand run along tho front of the fore-arm into 

 tho hand, ono lying under the other, and each divides into four 

 tendons ; those of tho snporficial ono aro inserted into tho 

 mMdlo bonos or phalanges of tho fingers, and those of the deep 

 into tho extreme phalanges ; just before the tendons of the 

 superficial ones are inserted, they are split, to allow the tendon 



of the deeper muscle to I*M through to the further phalanx, 

 mean* power and spaee are both economic*] The 

 of the tnnaelee are held in their place* at the wrict by 

 a circular band of fibrous tismte called the annular ligament 



In the lower extremity we find somewhat imilar aeta of 

 muMlee to those of the upper; but here, of ooune, the extensors 

 are on the front of the ley and thigh, and the flexor* at the 

 book ; the miuclM generally are nroeh larger than thoa* of the 

 arm. The mtuolea of the calf, the balk o( which U eompoeed 

 hut of ono, are inserted by the tando Achfllis into the bee), OB 

 which lover they draw powerfully in the various node* of pro. 

 groaaion. The arrangement of the annular ligament and of 

 too flexor tendons u similar to that of the band, with an 

 important exception, that the mnaelea do not diri-le into 

 tendons until much nearer their inaertion, aad are connected by 

 a strong slip with the flexor of the great toe. The reenlt of tin* 

 U that the fingers have much greater individuality of action 

 than tho toes ; for wbilut in the hand the thumb can be freely 

 bent without influencing tho fingers, in the foot, if the great to* 

 is flexed, all the toea bend w.- 



We must now paea on to the hut divUion of this portion of 

 our subject. 



THK NERVOUS SYSTEM. 



Tho nervous system ia generally described a* confuting of 

 two parts the cerebro-spinal system and the ganglionio or 

 sympathetic system. Each of these may be dirided into nerve 

 centre*, and nerve cords diverging from those centres to tnpply 

 tho different parts of the body. 



There are two lands of aervo structure, one ealled the white 

 matter or fibrous nervous matter, which is composed of two 

 kinds of fibres, and constitutes nearly the whole of the nb- 

 stance of the nerve cords, and also enter* largely into the 

 constitution of tho nerve centres ; the other, which in soft, of 

 -h-grey colour, called the vehicular or grey nenrooa 

 matter, is composed of vesicles or corpuscles, and is found 

 collected in masses in the great nerve centre* and the ganglia. 



The nerves aro round flattened cords, connected at one end 

 with the nerve centres, and dividing and subdividing nntfl they 

 are ultimately distributed to all parts of the body ; they are 

 divided according to their functions into two classes the 

 motor nerves, which are those that carry the mandate* of the 

 will to the parts they supply, and are thus the agents through 

 which all the movements of the body are performed : and the 

 sensory nerves, which carry back to the nerve centres the 

 impressions made by any stimulus at the scat of* their distri- 

 bution. By these the mind becomes conscious of all external 

 sensations. Tho sensory nerves include a sub-claw, tho nerve* 

 of special senso viz., tho nerves of hearing, seeing, tasting, 

 and smelling. 



The cerebro-spinal system consists of the spinal cord, the 

 brain, and the nerves proceeding from them. The spinal cord ia 

 a cylindrical mass of nerve matter ; in the adult it is usually 

 from sixteen to seventeen inches in length, and weighs, when 

 divested of its membranes and nerves, about an ounce and a 

 half; it occupies the upper two-thirds of the spinal canal, 

 extending from the occipital foramen above, through which 

 it is continuous, by a special portion called the medulla ob- 

 longata, with tho brain, to the first lumbar vertebra below. In 

 common with the brain, it is enclosed by three membrane*. Tho 

 external one, called the dura mater, which is a dense fibrous 

 structure of considerable strength, lines the inside of the 

 spinal canal and the bones of the skull. Closely inverting 

 the cord and brain is another membrane of a much moro 

 delicate texture, the pia mater; and interposed between this and 

 the dura mater is a thin, delicate membranous sac, containing 

 fluid called tho arachnoid (spider's web). If a section of the 

 spinal cord ia made it is found to be composed of the white 

 nervous matter, enclosing a comparatively small creecentJc maaa 

 of grey mattor. 



Prom tho sides of the cord are given off thirty-one pair* of 

 each of which arises from two roots. The rcots coming 

 from tho anterior portion of tho cord are motor ; thwe from 

 the posterior, on each of which is a ganglion, or collection of 

 grey matter, are sensory. Immediately after they emerge from 

 the sginal canal the two roots coalesce to form one nerve 

 cord, so that it follows that each of tho spinal nervwi is com- 

 pound, having both sensory and motor function*. The npper 

 cervical nerves join together to form what ia called a plexus, 



