CHAPTER IV. 



THE COMPARISON OF THE ANTERIOR EXTREMITY TO THE SPOKES OF A WHEEL CON- 

 SIDERED. ITS THREE CHARACTERS OF CRUTCH, PASSIVE TOOL, AND ACTIVE AU- 

 TOMATON. THE GREAT SERRATUS. ITS DOUBLE CHARACTER OF TENDON AM 

 MUSCLE. CENTRE OF MOTION. THE TRAPESIUS AND YELLOW CORD. LEVATOH 

 ANGULI SCAPULAE. TRACHELO SUBSCAPULARIS, ITS FUNCTION HITHERTO UNK\O\V> 

 THE GREAT DORSAL AND PECTORAL AS PROPELLERS. THE MASTOIDO HUME 

 RALIS AS AN EXTENSOR. THE MUSCLES OF THE SHOULDER-BLADE. THE P 

 OF MUSCLES THAT FLEX THE SHOULDER. THE FUNCTION OF THE TRICEPS 

 RESISTING THE FALL OF THE BODY AND IN LOCOMOTION. FUNCTION OF THE 

 FLEXORS OF THE FOREARM. HIGH ACTION. OBSTACLES TO A FULL UNDERSTAND 

 ING OF THE FUNCTIONS OF THE LOCOMOTIVE MUSCLES REMOVED BY THE CAM 

 ANALYSIS OF THE MOVEMENTS OF THE ANTERIOR EXTREMITY. MECHANICS 

 POINTS DESIRABLE IN A HORSE FOR SPEED OR STRENGTH. LOW CENTRES OF 

 MOTION. LONG LEVERS. COMPARISON BETWEEN THE ANTERIOR AND POSTERIOR 

 EXTREMITIES. WHY QUADRUPEDS RISE FROM RECUMBENT POSITIONS WITH DIFF 

 CULTY. WHY BOXERS AND OTHERS LIABLE TO BE PLACED SUDDENLY ON 

 DEFENCE HAVE THEIR LIMBS SEMI-FLEXED. ELEMENTS OF SPEED. 



THE anterior extremity furnishes a subject for the study of anirm 

 mechanics of more interest even than that which has demanded our 

 attention in the preceding chapters. 



There appear at first sight greater difficulties in the way 

 human ingenuity in the application of mechanical power for propul 

 sion to the anterior part of the trunk. The mind is led by the simili- 

 tudes of comparative anatomy, and the popular hypothesis of evolu- 

 tion from one common parentage, to look upon the anterior extrem- 

 ities as limbs in progress of development into arms or tool-makers. 

 The mind jumps, like the kangaroo, from the marsupials to the mon- 

 keys, to the orang-outang, and then to man by such easy leaps that 

 it is difficult to persuade one that he has advanced to his opinions 



without substantial 



grounds. 



To these causes must be ascribed th 



