PREHENSION. MANIPULATION. 198 



characteristic locomotive organs of birds, are sometimes, as in the penguins 

 and auks, modified by being shortened and provided only with short, stiff, 

 closed feathers, so as to act like fins, or paddles, especially in the movements 

 of diving and swimming beneath the surface. In the cursorial or running 

 birds, such as the cassowary, ostrich, and apteryx, the sternum is short, and 

 its keel absent ; the clavicles are small, attached firmly to the scapula? by bone, 

 but do not reach each other in front ; the clavicles are even sometimes absent ; 

 in these birds, the wing is small, or so rudimentary as to be wholly unlike a 



Prehension and Manipulation in Man. 



By far the most complicated prehensile instrument in animal me- 

 chanics, is the human upper limb ; and the singular perfection of all 

 its parts, and especially of its terminal segment, the hand, makes it 

 the most perfect manipulative organ with which we are acquainted, 

 and well fitted for the execution of the various designs and behests of 

 human ingenuity and will. The negative qualities of the human upper 

 limb, considered as a locomotive organ, constitute positive adaptations 

 for its prehensile and manipulative purposes. Amongst these, may be 

 mentioned the following: its smaller size, as compared with the lower 

 limb; the. sole bony attachment between the inner end of the clavicle, 

 and the sternum, so slight in comparison with the solid connection of 

 the pelvic bones with each other, and with the vertebral column ; the 

 consequent extreme mobility of the scapula and clavicle upon the 

 trunk, as contrasted with the immovability of the pelvis; the shallow 

 socket of the shoulder-joint, and the almost unlimited character of free 

 play of its movements, as contrasted with the deep hip-joint, and its 

 more restrained motions; the complex nature of the elbow-joint, and 

 especially the separate movements of the radius upon the ulna, for the 

 pronation and supination of the hand, as contrasted with the fixity of 

 the tibia and fibula; the lightness of the carpal bones, Fig. 53, 1 to 8, 

 as contrasted with the large size of those of the tarsus (compare Figs. 

 51 and 53) ; the articulation of the hand in a line with the forearm, 

 instead of at right angles, like that of the foot upon the leg ; the 

 greater length of the metacarpus, Fig. 53, 9, in relation to the carpus, 

 as contrasted with the more equal length of the tarsus and metatarsus, 

 Fig. 51 ; the standing out of the first metacarpal bone from the rest, 

 Fig. 53, so as to support the opposable thumb; the great relative length 

 of the phalanges of the fingers, 10, 11, 12, those of the middle finger 

 being about equal in length to the carpus and metacarpus together, 

 whilst, in the foot, the phalanges are not longer than the metatarsus 

 only ; and lastly, the superaddition of particular muscles, not repre- 

 sented in the lower limb, as for example the pronators and supinators 

 of the forearm, and certain special muscles, viz., the long extensors, 

 and the opponens, belonging to the thumb, and the proper long ex- 

 tensors of the fore and little fingers. The great toe, however, is also 

 well supplied with muscles, and possesses, in certain races, a slight 

 prehensile power. 



The' following details in the structure of the upper limb, require also 

 to be mentioned. The shallow socket on the outer angle of the scapula, 

 called the glenoid fossa, looks neither directly forwards nor outwards, 



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