ANATOMY AND PHYSIOLOGY. 



.09 



cartilages, articulations, and ligaments ; of which 

 seven belong to the neck, twelve to the back, and 

 five to the loins. In the centre of each vertebra 

 there is a hole fi :r the lodgment and continuation 

 of the spinal marrow, which extends from the 

 brain to the rump. From these vertebrae the 

 arched bones called ribs proceed ; and seven of 

 them join the breast-bone on each side, where 

 they terminate in cartilages, and form the cavity 

 of the thorax or chest. The five lower ribs, with 

 a number of muscles, form the cavity of the ab 

 domen, as above stated. The spine is one of 

 the most admirable mechanical contrivances in 

 the human frame. Had it consisted of only three 

 or four bones, or had the holes in each bone not 

 exactly corresponded and fitted into each other, 

 vhe spinal marrow would have been bruised, and 

 life endangered at every bending of the body. 

 The skull is composed often bones, and about 51 

 are reckoned to belong to the face, the orbits of 

 the eyes, and the jaws in which the teeth are 

 fixed. There are seldom more than 16 teeth in 

 each jaw, or 32 in all. The number of bones in 

 a human body is generally estimated at about 

 245 ; of which there are reckoned, in the skull, 

 head, and face, 61 ; in the trunk, 64 ; in the 

 arms, and hands, 60 , in the legs, and feet, 60. 

 The bones are provided with ligaments or hinges, 

 which bind and fasten them together, and pre 

 vent them from being displaced by any violent 

 motion ; and, that the ligaments may work 

 smoothly into one another, the joints are sepa 

 rated by cartilages or gristles, and provided with 

 a gland for the secretion of oil or mucus, which 

 is constantly exuding into the joints ; so that 

 every requisite is provided by our benevolent 

 Creator, to prevent pain, and to promote facility 

 of motion. In considering the joints,&quot; says 

 Dr. Paley, &quot; thoe is nothing, perhaps, which 

 ought to move our gratitude more than the re 

 flection, how well they wear. A limb shall swing 

 upon its hinge or play in its socket many hun 

 dred times in an hour, for 60 years together, 

 without dimlnu .ion of agility ; which is a long 

 time for any thing to last for any thing so much 

 worked aa the joints are.&quot; 



The Muscular System. A muscle is a bundle 

 of fleshy, and sometimes of tendinous fibres. 

 The fleshy fibres compose the body of the muscle ; 

 and the tendinous fibres the extremities. Some 

 muscles are long and round ; some plain and cir 

 cular ; some are spiral, and some have straight 

 fibres. Some are double, having a tendon run 

 ning through the body from head to tail ; some 

 have two or more tendinous branches running 

 through, with various rows and orders of fibres. 

 All these, and several other varieties, are essen 

 tially requisite for the respective offices they have 

 to perform in the animal system. The muscles 

 constitute the fleshy part of the human body, 

 n .nd give it that varied and beautiful form we ob 

 serve over all its surface. But their principal 



design is to serve as the organs of motion. They 

 are inserted, by strong tendinous extremities, 

 into the different bones of which the skeleton is 

 composed ; and, by their contraction and disten- 

 tion, give rise to all the movements nf the body. 

 The muscles, therefore, may be considered as so 

 many cords attached to he bones , and the Author 

 of nature has fixed them according to the most 

 perfect principles of mechanism, so as to produce 

 the fittest motions in the parts for the movement 

 of which they are intended. 



One of the most wonderful properties of the 

 muscles is, the extraordinary force they exert, 

 although they are composed of such slender 

 threads or fibres. The following facts, in rela 

 tion to this point, are demonstrated by the cele 

 brated Borelli, in his work, &quot; De Motu Ani- 

 malium.&quot; When a man lifts up with his teeth a 

 weight of 200 pounds, with a rope fastened to 

 the jaw-teeth, the muscles named temporal and 

 masseter, with which people chew, and which per 

 form this work, exert a force of above 15,0001bs. 

 weight. If any one hanging his arm directly 

 downwards lifts a weight of 20 pounds, with the 

 third or last joint of his thumb, the muscle which 

 bends the thumb and bears that weight exerts a 

 force of about three thousand pounds. When a 

 man, standing upon his feet, leaps or springs up 

 wards to the height of two feet, if the weight of 

 such a man be 150 pounds, the muscles employed 

 in that action will exert a force 2000 times great 

 er; that is to say, a force of about three hundred 

 thousand pounds. The heart, at each pulse or 

 contraction, by which it protrudes the blood out 

 of the arteries into the veins, exerts a force of 

 above a hundred thousand pounds. Who can 

 contemplate this amazing strength of the mus 

 cular system, without admiration of the power 

 and wisdom of the Creator, who has thus endued 

 a bundle of threads, each of them smaller than 

 a hair, with such an astonishing degree of me 

 chanical force ! There have been reckoned about 

 446 muscles in the human body, which have been 

 dissected and distinctly described ; every one of 

 which is essential to the performance of some 

 one motion or other, which contributes to our 

 ease and enjoyment ; and, in most instances, a 

 great number of them is required to perform their 

 different functions at the same time. It has 

 been calculated, that about a hundred muscles are 

 employed every time we breathe. &quot; Breathing 

 with ease,&quot; says Dr. Paley, &quot; is a blessing of 

 every moment ; yet, of all others, it is that which 

 we possess with the least consciousness. A man 

 in an asthma is the only man who knows how to 

 estimate it.&quot; 



The Heart and Blood-vessels. The heart is 

 a hollow muscular organ, of a conical shape, and 

 consists of four distinct cavities. The two larg 

 est are called ventricles, and the two smallest 

 auricles. The ventricles send out the blood to 

 the arteries ; the auricles receive it from the 



