ULNA. 77 



and excluded from the \vrist-joint by an inter-articular fibro- 

 cartilage. 



The superior extremity presents a semilunar concavity of large 

 size, the greater sigmaid notch, for articulation with the humerus ; 

 and upon the outer side a lesser sigmoid notch, which articulates 

 with the head of the radius. Bounding the greater sigmoid notch 

 posteriorly is the olecranon process ; and overhanging it in front, a 

 pointed eminence with a rough triangular base the coronoid process. 

 Behind the lesser sigmoid notch, and extending downwards on the 

 side of the olecranon, is a triangular rough surface, for the an- 

 coneus muscle ; and upon the posterior surface of the olecranon 

 another triangular surface, which is subcutaneous. . 



The shaft is prismoid in form, and presents three surfaces, an- 

 terior, posterior, and internal ; and three borders. The anterior 

 surface is occupied by the flexor profundus digitorum for the upper 

 three-fourths of its extent ; and below by a depression, for the pro- 

 nator quadratus muscle. A little above its middle is the nutritious 

 foramen, which is directed upwards. Upon the posterior surface at 

 the upper part of the bone is the triangular rough depression for the 

 anconeus muscle, bounded inferiorly by an oblique ridge which 

 runs downwards from the posterior extremity of the lesser sigmoid 

 notch. Below the ridge the surface is marked into several grooves, 

 for the attachment of the extensor ossis metacarpi, extensor secundi 

 internodii, and extensor indicis muscle. The internal surface is 

 covered in for its whole extent by the flexor carpi ulnaris. 

 The anterior border is rounded, and gives origin by its lower fourth 

 to the pronator quadratus; the posterior is more prominent, and 

 affords attachment to the flexor carpi ulnaris and extensor carpi 

 ulnaris. At its upper extremity it expands into the triangular sub- 

 cutaneous surface of the olecranon. The external or radial border 

 is sharp and prominent, for the attachment of the interosseous 

 membrane. 



The lower extremity terminates in a small rounded head, from the 

 side of which projects the styloid process. Upon the posterior 

 surface of the head is a groove, for the tendon of the flexor carpi 

 ulnaris ; and upon the side opposite to the styloid process a smooth 

 surface, for articulation with the side of the radius. 



Developement. By/owr centres ; one for the shaft, one for each 

 extremity, and one for the olecranon. 



Articulations. With two bones ; the humerus and radius. 



Attachment of Muscles. To twelve; by the olecranon, to the 

 triceps extensor cubiti, one head of the flexor carpi ulnaris, and to 

 the anconeus ; by the coronoid process, to the brachialis anticus, 

 pronator radii teres, flexor sublimis digitorum, and flexor profundus 

 digitorum ; by the shaft, to the flexor profundis digitorum, flexor 

 carpi ulnaris, pronator quadratus, anconeus, extensor carpi ulnaris, 

 extensor ossis metacarpi pollicis, extensor secundi internodii pollicis, 

 and extensor indicis. 



RADIUS. The radius is the rotatory bone of the fore-armpit is di- 



