The common frog . widely different from the adult in its muscular(or myological) furniture, and this for one obviousreason. Muscles are, as we have shown,/^r excellence, organs of motion, and the motions of the tadpoleare essentially different from those of the frog. The frog, as all know, progresses on land by jumps,and swims through the water by a series of move-ments which are in fact aquatic jumps. This actionis familiar to many of us, not only from observationbut also by imitation (the frog being a swimming-master given us by nature), but it is none the less amode of swimming which is ver
The common frog . widely different from the adult in its muscular(or myological) furniture, and this for one obviousreason. Muscles are, as we have shown,/^r excellence, organs of motion, and the motions of the tadpoleare essentially different from those of the frog. The frog, as all know, progresses on land by jumps,and swims through the water by a series of move-ments which are in fact aquatic jumps. This actionis familiar to many of us, not only from observationbut also by imitation (the frog being a swimming-master given us by nature), but it is none the less amode of swimming which is very exceptional indeed. The tadpole progresses through the w^ater in a verydifferent manner, namely, by lateral undulations of its VIF.] THE COMMON FROG. 97 tail, which is the usual mode of swimming amongvertebrate animals—that made use of by sharks andporpoises, as well as by the overwhelming majority offishes. Studying the life-history of this one animal, then,we become acquainted with a process of direct tran-. FiG. 60.—Anterior muscles of the Trunk of Man : the pectorahs major of the rij^htside the left external oblique being removed, i, pectoraiis major : 2, pec-toralis minor ; 3, subclavius ; 4, serratus magnus ; 5, internal intercostals ; 6,external oblique ; 7, internal oblique ; 8, linea alba. sition from the condition of a fish to that of a quad-ruped, as regards a most important group of organs. In ourselves, the back is provided with muscleswhich extend along its length in a complex series oflongitudinal divisions, from the middle line outwards. The abdomen of man is inclosed and protected bysuccessive layers laid one upon another, the H 98 THE COMMON FROG. [chap. fibres of the successive muscles being differentlydirected. Thus we have (i) the external oblique (thefibres of which pass obliquely downwards and back-wards), (2) the internal oblique (the fibres of whichpass obliquely downwards and forwards), (3) theTraiisveisalis (with transverse fibres
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