216 MODIFICATIONS OF THE HUMAN SKELETON 



tebral" substance, rests between the bodies of the verte- 

 brae. The distribution and libration of the trunk, with 

 the superadded weight of the head and arms, are favored 

 by these gentle curves, and the shock in leaping is broken 

 and diffused by the numerous elastic intervertebral joints. 

 The expansion of the cranium behind, and the shortening 

 of the face in front, give a globe-like form to the skull, 

 which is poised by a pair of condyles, advanced to near 

 the middle of its base upon the cups of the atlas ; so that 

 there is but a slight tendency to incline forwards when 

 the balancing action of the muscles ceases, as when the 

 head nods during sleep in an upright posture. 



The framework of the upper extremity shows all the 

 perfections that have been superinduced upon it in the 

 mammalian series, viz: a complete clavicle, 58, antibra- 

 chial bones, 54, 55, with rotatory movements as well as 

 those of flexion and extension, and the five digits, 57, 

 free and endowed with great extent and variety of move- 

 ments: of these, the innermost, which is the first to 

 shrink and disappear in the lower mammalia, is in man 

 the strongest, and is modified to form an opposable thumb 

 more powerful and effective than in any of the quadru- 

 mana. The scapula, 51, presents an expanded surface of 

 attachment for the muscles which work the arm in its 

 free socket ; the humerus, 53, exceeds in length the bones 

 of the fore-arm. The carpal bones, 56, are eight in num- 

 ber, called scaphoides, lunare, cuneiforme, pisiforme, tra- 

 pezium, trapezoides, magnum, and unciforme: of these 

 the scaphoid and unciforme are compound bones ; i. e. 

 they consist each of two of the bones of the type-carpus, 

 connate. 



In the human skull, viewed in relation to the arche- 

 type, as exemplified in the fish and the crocodile, the fol- 



