SKELETON AND TEETH 83 



pressed together, with very little movement between them, and 

 are arranged in two transverse rows. The upper row con- 

 tains four bones, which enumerating from the inner side are 

 the scaphoid, lunar, pyramidal (or cuneiform) and pisiform. 

 The scaphoid and lunar support the radius, while the ulna 

 rests upon the pyramidal. The pisiform, though very con- 

 stantly present, is not a true carpal, but an ossification in 

 the tendon of one of the flexor miiscles, which close the fingers ; 

 it projects more or less prominently backward and articulates 

 with the ulna and pyramidal. The second row is also made 

 up of four bones, which, from within outward, are the trape- 

 zium, trapezoid, magnum and unciform. The relations of the 

 two rows vary much in different mammals and the arrange- 

 ment may be serial ot alternating; thus, the scaphoid rests 

 upon the trapezium and trapezoid and usually covers part of 

 the magnum ; the lunar may rest upon the magnum only, 

 but very much more frequently is equally supported by the 

 magnum and unciform and the pyramidal by the latter only. 

 The ninth carpal is the central, which, when present and dis- 

 tinct, is a small bone, wedged in between the two rows. Few 

 existing mammals have a separate central, which, though 

 present in the embryo, has coalesced with the scaphoid in the 

 great majority of forms. In the more advanced and differ- 

 entiated mammals the number of carpals may be consider- 

 ably reduced by the coossification of certain elements or 

 the complete suppression and loss of others. In all existing 

 Carnivora and a few other mammals the scaphoid and lunar 

 are united in a compound element, the scapho-lunar (or, more 

 accurately, the scapho-lunar-central) ; hoofed animals with 

 a diminished number of toes generally lose the trapezium, 

 and other combinations occur. ' The second row of carpals 

 carries the metacarpals, and primitively the trapezium, trape- 

 zoid and magnum are attached each to one metacarpal and 

 the unciform has two. 



The metacarpus consists typically of five members^ a num- 



