COMPARATIVE STUDY OF MOTION. 597 



at different times, and always diagonally one after the other; for example, in the 

 horse, right fore, left hind; left fore, right hind. In trotting there is an accelera- 

 tion of this gait, so that the legs are moved together diagonally at two different 

 times, while the body is at the same time raised higher. In the interval between 

 both hoof-beats the 'body is in the air half the time in ordinary trotting, longer 

 in an extended trot. 



The gallop: When a (right) galloping horse moves horizontally through 

 the air, the left hind foot comes down first. Shortly afterward the left fore 

 foot and the right hind foot come down simultaneously; the right fore 

 foot has not yet reached the ground, and is directed far forward. Up to this 

 point the body has maintained its horizontal position. When, however, a 

 few moments later, the left hind foot leaves the ground, it is at a higher level 

 than the fore foot; at the same time, the right fore foot is also brought down and 

 placed far forward; the right hind leg and the left fore leg are in extreme exten- 

 sion. At the next moment these limbs also leave the ground, and the hind foot 

 acquires such an ascendency over the fore foot that it comes to be situated much 

 higher than the latter. The body, therefore, is thrown forward and downward 

 until the right fore leg, which alone still touches the ground, contracts actively, 

 and pushes the body forcibly from the ground. When this has occurred, the 

 horse again soars in air with the body directed horizontally. In galloping the 

 longitudinal axis of the horse's body is placed obliquely to the direction of the 

 movement, forming an acute angle. In an extended gallop (carriere), which is 

 really a continuous jumping motion, the right hind leg and the left fore leg, for 

 example, do not reach the ground simultaneously, the former striking first. The 

 rapidity of this movement in the horse is 82 feet a second. Most beasts of prey, 

 hares, etc.. employ only the carriere for rapid movements. 



The amble is a modification of the gait that is peculiar to many animals, 

 for example the camel, the giraffe, the elephant. It occurs also in dogs and in 

 horses, but it is not a favorite gait with the latter. It consists in advancing 

 both feet on the same side simultaneously or almost so. 



I.Iarey fastened compressible ampullae under the hoofs of the horse, connecting 

 them with registering apparatus; and thus accurately recorded the time-relations 

 of the various gaits. Muybridge, in 1872 , was the first to obtain series of instanta- 

 neous photographs of running horses, which Schmidt-Mulheim placed together in 

 the stroboscope. 



In snakes the progression of the body is secured by elevation and depression 

 of the ribs in a manner resembling rowing. 



Swimming is an acquired art on the part of man. The specific gravity of 

 the whole body is, on an average, somew r hat higher than that of river-water, 

 though somewhat lower than that of sea-water. In the quiet dorsal decubitus, 

 with only the mouth and the nose above the surface of the water, sinking can 

 be prevented by slight downward pressing movements of the hands ; sometimes no 

 movement at all may be necessary. In this position progression may be accom- 

 plished by simple extension and adduction of the legs. The movement may be 

 accelerated by oar-like strokes with the arms. Swimming on the abdomen is 

 more difficult, because the head, being held above water, increases the specific 

 weight of the body. The body is advanced and held above water by movements 

 divided into the following three phases: First phase, horizontal rowing movement 

 of the extended arms from before backward to the horizontal position (forward 

 movement) ; second phase, downward pressure of the arms toward the depth, 

 with subsequent adduction of the elbows to the bod}'' (elevation of the body) , 

 together with a drawing up of the extended legs; third phase, forward thrust of 

 the arms, in contact with each other, and at the same time extension and ad- 

 duction of the legs obliquely backward and toward the depth, as a result of which 

 both elevation of the body and forward progression are effected. Unduly rapid 

 movements are exhausting and defeat their own purpose. Special attention should 

 be paid to suitable respiratory movements. 



Many land mammals, whose bodies are specifically lighter than water, move 

 through it with a walking motion, especially of the hind legs; at the same time 

 the feet, being directed downward, assure the normal position of the body, as 

 they are specifically the heaviest parts of the body. Those mammals that live 

 much in the water, as well as reptiles and amphibia, possess webbed feet and 

 a propelling tail partly resembling that of fish. Whales resemble fish in the 

 external appearance of their bodies. 



Fish primarily make use of their tail as a motor organ, which is moved by 



