CARPUS. 219 



Development (Fig. 160). Ky three centres, one for the shaft, and one for each 

 extremity. That for the shaft makes its appearance near the centre of the 

 bone, soon after the development of the humerus commences. At birth the 

 shaft is ossified, but the ends of the bone are cartilaginous. About the end of 

 the second year, ossification commences in the lower epiphysis ; and about the 

 fifth year, in the upper one. At the age of puberty, the upper epiphysis 

 becomes joined to the shaft ; the lower epiphysis becoming united about the 

 twentieth year. 



Articulations. With four bones the humerus, ulna, scaphoid, and semilunar. 



Attachment of Muscles. To the tuberosity, the Biceps; to the oblique ridge, 

 the Supinator Brevis, Flexor Digitorum Sublimis, and Flexor Longus Pollicis ; 

 to the shaft (its anterior surface), the Flexor Longus Pollicis and Pronator 

 Quadratus ; (its posterior surface), the Extensor Ossis Metacarpi Pollicis and 

 Extensor Primi Internodii Pollicis; (its outer surface), the Pronator Radii 

 Teres ; and to the styloid process, the Supinator Longus. 



The Hand is subdivided into three segments -the Carpus or "Wrist, the Meta- 

 carpus or Palm, and the Phalanges or Fingers. 



THE CARPUS. 



The bones of the Carpus, eight in number, are arranged in two rows. Those 

 of the upper row, enumerated from the radial to the ulnar side, are the scaphoid, 

 semilunar, cuneiform, and pisiform ; those of the lower row, enumerated in the 

 same order, are the trapezium, trapezoid, os magnum, and unciform. 



Common Characters of the Carpal Bones. Each bone (excepting the pisiform) 

 presents six surfaces. Of these, the anterior or palmar, and the posterior or 

 dorsal, are rough, for ligamentous attachment, the dorsal surface being generally 

 the broader of the two. The superior and inferior are articular, the superior 

 generally convex, the inferior concave ; and the internal and external are also 

 articular when in contact with contiguous bones, otherwise rough and tuber- 

 cular. Their structure in all is similar, consisting within of cancellous tissue 

 inclosed in a layer of compact bone. Each bone is also developed from a 

 single centre of ossification. 



BONES OF THE UPPER Bow. (Figs. 161, 162.) 



The Scaphoid is the largest bone of the first row. It has received its name 

 from its fancied resemblance to a boat, being broad at one end, and narrowed 

 like a prow at the opposite. It is situated at the upper and outer part of the 

 carpus, its direction being from above downwards, outwards, and forwards. 

 The superior surface is convex, smooth, of triangular shape, and articulates 

 with the lower end of the radius. The inferior surface, directed downwards, 

 outwards, and backwards, is smooth, convex, also triangular, and divided by a 

 slight ridge into two parts, the external of which articulates with the trape- 

 zium, the inner with the trapezoid. The posterior or dorsal surface presents a 

 narrow, rough groove, which runs the entire breadth of the bone, and serves 

 for the attachment of ligaments. The anterior or palmar surface is concave 

 above, and elevated at its lower and outer part into a prominent rounded 

 tubercle, which projects forwards from the front of the carpus, and gives attach- 

 ment to the anterior annular ligament of the wrist. The external surface is 

 rough and narrow, and gives attachment to the external lateral ligament of the 

 wrist. The internal surface presents two articular facets : of these, the superior 

 or smaller one is flattened, of semilunar form, and articulates with the semi- 

 lunar ; the inferior or larger is concave, forming with the semilunar bone, a 

 concavity for the head of the os magnum. 



To ascertain to which hand this bone belongs, hold the convex radial articu- 

 lar surface upwards, and the dorsal surface backwards; the prominent tubercle 

 will be directed to the side to which the bone belongs. 



