. The Bible and science. Fig. 89.—A front view of the sternum, St, with the cartilages of the ribs, R\ andparts of the ribs themselves, R. The various pieces of this bony skeleton are movedupon one another by means of muscles. These muscles,known to us commonly under the name of flesh, con-sist of bundles of contractile threads, or fibrils, which 174 MUSCLES—NERVES, MOTOR AND SENSORY. have the power of shortening, on the application ofcertain stimuli. This may be noticed by anyone in themuscles of the ball of the thumb. On striking themsharply with the back of a taLle knife they may beseen sli
. The Bible and science. Fig. 89.—A front view of the sternum, St, with the cartilages of the ribs, R\ andparts of the ribs themselves, R. The various pieces of this bony skeleton are movedupon one another by means of muscles. These muscles,known to us commonly under the name of flesh, con-sist of bundles of contractile threads, or fibrils, which 174 MUSCLES—NERVES, MOTOR AND SENSORY. have the power of shortening, on the application ofcertain stimuli. This may be noticed by anyone in themuscles of the ball of the thumb. On striking themsharply with the back of a taLle knife they may beseen slightly to contract, and the thumb to is much more evident if a current of electricity bepassed through them, but the usual way in which theyare made to contract is by a stimulus wdiich they re-ceive from their Fig. 90.—The Bones of the Uiiper Extremity with the Biceps Muscle. The two tendons by which this muscle is attached to the scai)ula, oi shoulder-blade,are seen at a. p indicates the attachment of the to the radius, andht nee the point of action of the power ; f, the fulcrums, the lower end of thehumerus on which the upper end of the radius (togetlier with the ulnaa) moves ;w, the weight (of tlie hand). To each muscle, one or more motor nerves passdown from the spinal cord, and by them the muscleis set in action. One of the commonest occasions ofthe action of muscle is the stimulation of a sensorynerve, and yet sensory nerves have no direct SPINAL CORD—REFLEX ACTION—BRAIN. 175 connection with muscles, nor any power to makethem contract. The sensory nerves are, however, indirectly con-nected with muscles through the spinal cord. Fromall parts of the spinal cord motor nerves pass to themuscles, and to all parts of the spinal cord, sensorynerves pass from the skin. When one
Size: 1875px × 1333px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, booksubjectnaturalhistory, booky
