4 8 



GENERAL ANATOMICAL CHARACTERS 



its anterior surface, and the two bones, instead of being external 

 and internal, are anterior and posterior. In many hoofed or Ungu- 

 late mammals, and in Bats, the ulna is reduced to little more than 

 its upper articular extremity, and firmly ankylosed to the radius 

 — stability of these parts being more essential than mobility. 



Manas. — The terminal segment of the anterior limb is the hand 

 or maims. Its skeleton consists of three divisions : (1) the 

 " carpus," a group of small, more or less rounded or angular bones 

 with flattened surfaces applied to one another, and, though arti- 

 culating by synovial joints, having scarcely any motion between 

 them ; (2) the " metacarpus," a series of elongated bones placed side 

 by side, with their proximal ends articulating by almost immovable 

 joints with the carpus; (3) the "phalanges" or bones of the digits, 

 usually three in number to each, articulating to one another by freely 

 movable hinge- joints, the first being connected in like manner to 

 the distal end of the metacarpal bone to which it corresponds. 



Carpus. — To understand thoroughly the arrangement of the 

 bones of the carpus in mammals, it is necessary to study their 

 condition in some of the lower vertebrates. Fig. 17 represents 

 the manus in one of its fullest and at the same time most 



generalised forms, as seen in one of the 

 Water Tortoises (Chelydra serpentina). The 

 carpus consists of two principal rows of 

 bones. The upper or proximal row con- 

 tains three bones, to which Gegenbaur 

 has applied the terms radiate (r), inter- 

 medium (i), and uhiare (u), the first being 

 on the radial or preaxial side of the limb. 1 

 The lower or distal row contains five 

 bones, called carpale 1, 2, 3, 4, and 5 

 respectively, commencing on the radial 

 side. Between these two rows, in the 

 middle of the carpus, is a single bone, 

 the centrate (c). In this very symmetrical 

 carpus it will be observed that the radiate 

 supports on its distal side two bones, 

 carpale 1 and 2 ; the intermedium is in a 

 line with the centrate and carpale 3, which 

 together form a median axis of the hand, 

 while the ulnare has also two bones articu- 

 lating with its distal end, viz. carpale 4 

 and 5. Each of the carpals of the distal 

 row supports a metacarpal. 



1 The opinion has recently been expressed by Baur that the bone termed 

 radiale in Fig. 17 is really a second centrale, and that the radiale is represented 

 by a minute bone generally known as the radial sesamoid. The mammalian 



Fio. 17.— Dorsal surface of the 

 right inarms of a Water Tortoise 

 (Chelydra serpentina). After Ge- 

 genbaur. U, Ulna ; R, radius ; u, 

 ulnare ; i, intermedium ; r, radiale ; 

 c, centrale ; 1-5, the five bones of 

 the distal row of the carpus ; mi- 

 ni 5 , the five metacarpals. 



