136 OSTEOLOGY. 



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 for- 

 wards, 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 examina- 

 tion three borders, and three surfaces. 



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

 noid 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 attachment 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 triangular 

 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 with 

 the middle third of the bone, is the nutritious canal, directed obliquely upwards 

 and inwards. 



The posterior surface, directed backwards and outwards, is broad and concave 

 above, somewhat narrower and convex in the middle of its course, narrow, smooth, 

 and rounded below. It presents above, an oblique ridge, which runs from the 

 posterior extremity of the lesser sigmoid cavity, downwards to the posterior 

 border ; the triangular surface above this ridge receives the insertion of the An- 

 coneus muscle, whilst the ridge itself affords attachment to the Supinator brevis. 

 The surface of bone below this is subdivided by a longitudinal ridge into two 

 parts ; the internal part is smooth, concave, and gives origin to, occasionally is 

 merely covered by, the Extensor carpi ulnaris. The external portion, wider and 

 rougher, gives attachment from above downwards to part of the Supinator brevis, 

 the Extensor ossis metacarpi pollicis, the Extensor secundi internodii pollicis, and 

 the Extensor indicis muscles. 



The internal surface is broad and concave above, narrow and convex below. 

 It gives attachment by its upper three-fourths to the Flexor profundus digitorum 

 muscle ; its lower fourth is subcutaneous. 



The Lower Extremity of the ulna is of small size, and excluded from the articu- 

 lation of the wrist-joint. It presents for examination two eminences ; the outer 

 and larger is a rounded articular eminence, termed the head of the ulna, The 

 inner, narrower and more projecting, is a non- articular eminence, the styloid 

 process. The head presents an articular facet, part of which, of an oval form, is 

 directed downwards, and plays on the surface of the triangular fibre-cartilage, 

 which separates this bone from the wrist-joint ; the remaining portion, directed 



