CAUPUS. 



79 



Fisr. 31.* 



Immediately in front of the styloid process is a groove, which 

 lodges the tendons of the extensor ossis metacarpi pollicis, and ex- 

 tensor primi internodii; and behind the process a broader groove, 

 for the tendons of the extensor carpi radialis longior and brevior, and 

 extensor secundi internodii ; behind this is a prominent ridge, and a 

 deep and narrow groove, for the tendon of the extensor indicis ; and 

 still farther back part of a broad groove, completed by the ulna, for 

 the tendons of the extensor communis digitorum. 



Developement. By three centres ; one for the shaft, and one for 

 each^ extremity. 



Articulations. With four bones; humerus, ulna, scaphoid, and 

 semilunar. 



Attachment of Muscles. To nine; by the tuberosity and oblique 

 ridge, to the biceps, supinator brevis, pronator radii teres, flexor sub- 

 limis digitorum, and pronator quadratus ; by the anterior surface, to 

 the flexor longus pollicis and pronator quadratus ; by the posterior 

 surface, to the extensor ossis metacarpi pollicis, and extensor primi 

 internodii ; and by the styloid process, to the supinator longus. 



CARPUS. The bones of the carpus are eight in number, they are 

 arranged in two rows. In the first row, commencing from the 

 radial side, are the os scaphoides, semilunare, cuneiforme, pisiforme ; 

 and in the second row, in the same order, the os trapezium, trape- 

 zoides, os magnum and unciforme. 



The scaphoid bone is named from bear- 

 ing some resemblance to the shape of a 

 boat, being broad at one end, and nar- 

 rowed like a prow at the opposite, con- 

 cave on one side, and convex upon the 

 other. It is, however, more similar in 

 form to a cashew nut, flattened and con- 

 cave upon one side. If carefully examined, 

 it will be found to present a convex and a 

 concave surface, a convex and a concave 

 border, a broad end, and a narrow and 

 pointed extremity the tuberosity. 



To ascertain to which hand it belongs, 

 let the student hold it horizontally, so that 

 the convex surface may look backwards 

 (L e. towards himself,) and the convex bor- 

 der upwards: the broad extremity will indicate its appropriate 



* A diagram showing the dorsal surface of the bones of the carpus, with their articu- 

 lations. The right hand. R. The lower end of the radius. U. The lower extremity 

 of the ulna. F. The inter-articular fibre-cartilage attached to the styloid process of 

 the ulna, and to the margin of the articular surface of the radius. S. The scaphoid 

 bone : the numeral (5) indicates the number of bones with which it articulates. L. 

 The semilunare articulating with five bones. C. The cuneiforme, articulating with 

 three bones. P. The pisiforme, articulating with the cuneiforme only. T. The first 

 bone of the second row the trapezium, articulating with four bones. T. The second 

 bone the trapezoides, articulating also with four bones. M. The os magnum, articu- 

 lating with seven. U. The unciforme articulating with five. The numerals, 1, 3, 1, 

 2, 1, on the metacarpal bones, refer to the number of their articulations with the car- 

 pal bones. 



