214 THE SKELETON. 



of this surface with the shaft is a rough eminence, the tubercle of the ulna, for 

 the attachment of the oblique ligament. Its outer surface presents a narrow, 

 oblong, articular depression, the lesser sigmoid cavity. The inner surface, by 

 its prominent free margin, serves for the attachment of part of the internal 

 lateral ligament. At the front part of this surface is a small rounded eminence 

 for the attachment of one head of the Flexor Digitorum Sublimis, behind the 

 eminence, a depression for part of the origin of the Flexor Profundus Digito- 

 rum, and, descending from the eminence, a ridge, which gives attachment to 

 one head of the Pronator Eadii Teres. Occasionally the Flexor Longus Pol- 

 licis arises from the lower part of the coronoid process by a rounded bundle 

 of muscular fibres. 



The greater sigmoid cavity, so called from its resemblance to the old shape of 

 the Greek letter s, is a semilunar depression of large size, formed by the ole- 

 cranon and coronoid processes, and serving for articulation with the trochlear 

 surface of the humerus. About the middle of either lateral border of this 

 cavity is a notch, which contracts it somewhat, and serves to indicate the junc- 

 tion of the two processes of which it is formed. The cavity is concave from 

 above downwards, and divided into two lateral parts by a smooth elevated 

 ridge, which runs from the summit of the olecranon to the tip of the coronoid 

 process. Of these two portions, the internal is the larger ; it is slightly concave 

 transversely, the external portion being nearly plane from side to side. 



The lesser sigmoid cavity is a narrow, oblong, articular depression, placed on 

 the outer side of the coronoid process, and serving for articulation with the 

 head of the radius. It is concave from before backwards ; and its extremities, 

 which are prominent, serve for the attachment of the orbicular ligament. 



The Shaft is prismatic in form at its upper part, and curved from behind 

 forwards, and from within outwards, so as to be convex behind and externally; 

 its central part is quite straight ; its lower part rounded, smooth, and bent a 

 little outwards ; it tapers gradually from above downwards, and presents for 

 examination three borders, and three surfaces. 



The anterior border commences above at the prominent inner angle of the 

 coronoid process, and terminates below in front of the styloid process. It is 

 well marked above, smooth and rounded in the middle of its extent, and affords 

 attachment to the Flexor Profundus Digitorum: sharp and prominent in its 

 lower fourth for the attachment of the Pronator Quadratus. It separates the 

 anterior from the internal surface. 



The posterior border commences above at the apex of the triangular surface 

 at the back part of the olecranon, and terminates below at the back part of the 

 styloid process; it is well marked in the upper three-fourths, and gives attach- 

 ment to an aponeurosis common to the Flexor Carpi Ulnaris, the Extensor 

 Carpi Ulnaris, and the Flexor Profundus Digitorum muscles ; its lower fourth 

 is smooth and rounded. This border separates the internal from the posterior 

 surface. 



The external border commences above by two lines, which converge one from 

 each extremity of the lesser sigmoid cavity, inclosing between them a triangu- 

 lar space for the attachment of part of the Supinator Brevis, and terminates 

 below at the middle of the head of the ulna. Its two middle fourths are very 

 prominent, and serve for the attachment of the interosseous membrane; its 

 lower fourth is smooth and rounded. This border separates the anterior from 

 the posterior surface. 



The anterior surface, much broader above than below, is concave in the upper 

 three-fourths of its extent, and affords attachment to the Flexor Profundus Digi- 

 torum; its lower fourth, also concave, to the Pronator Quadratus. The lower 

 fourth is separated from the remaining portion of the bone by a prominent 

 ridge, directed obliquely from above downwards and inwards; this ridge marks 

 the extent of attachment of the Pronator above. At the junction of the upper 



