204 SKELETON. 



The bones of the upper extremity are much less robust than 

 those of the lower, a very certain indication of the difference of 

 the uses for which they were intended. Their articular surfaces 

 are arranged for great variety and extent of motion, in the 

 seizing and handling of bodies; whereas in the lower extremity, 

 they are fashioned so as to suit the comparatively limited num- 

 ber of motions requisite to progression, and to sustain the body 

 firmly in the upright position. The carpus and metacarpus are 

 much smaller than the tarsus and the metatarsus, because the 

 latter are intended to support a great weight. On the contrary, 

 the phalanges of the fingers are much better developed than the 

 phalanges of the toes, because the latter are not destined to hold 

 bodies and to examine them, and may be dispensed with both 

 in standing and in progression. 



The motions of the upper extremity are immensely varied, 

 and by a short attention to them, some useful hints may be ob- 

 tained in regard to dislocations. 



SECT. VII. OF THE MOTIONS OF THE SHOULDER. 



The clavicle performs a very important office in the actions 

 of the shoulder, by preserving it in a fit attitude for the motions 

 of the upper extremity. The simple movements of the clavicle, 

 of which the sterno-clavicular articulation is the centre, are 

 those of elevation, depression, advancing, and retreating, and a 

 rapid succession of these produces circumduction. The weight 

 of the shoulder is also sustained by the clavicle, by the latter 

 being fastened at the extremity next to the sternum, and having 

 in the cartilage of the first rib a fulcrum, intermediate to this 

 attachment and to the weight at its other end. This is proved 

 conclusively by its fracture; for in that case the shoulder inva- 

 riably falls down, from the lever being broken which kept 

 it up. 



The clavicle, also, by keeping the glenoid cavity at a dis- 

 tance from the side of the thorax, and directed outwards, gives 

 great facility and latitude to certain motions in the human sub- 

 ject; and which are performed with difficulty, and very imper- 

 fectly, in animals not having a clavicle. A principal one of 

 these motions is circumduction, manifested by the elbow being 



