152 THE SKELETON. 



The Coronoid Process (xopcovq, anything hooked like a crow's beak) is a trian- 

 gular eminence of bone which projects horizontally forward from the upper and 

 front part of the ulna. Its base is continuous with the shaft, and of considerable 

 strength ; so much so that fracture of it is an accident of rare occurrence. Its 

 apex is pointed, slightly curved upward, and received into the coronoid depression 

 of the humerus in flexion of the forearm. Its upper surface is smooth, concave, 

 and forms the lower part of the greater sigmoid cavity. The under surface is con- 

 cave, and marked internally by a rough impression for the insertion of the 

 Brachialis anticus. At the junction of this surface with the shaft is a rough emi- 

 nence, 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 attach- 

 ment 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 sublimis 

 digitorum ; behind the eminence, a depression for part of the origin of the Flexor 

 profundus digitorum ; and, descending from the eminence, a ridge which gives 

 attachment to one head of the Pronator radii teres. Grenerallv, the Flexor lono-us 



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pollicis has an origin 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 2', is a semilunar depression of large size, formed by the olecranon 

 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 junction of the two 

 processes of which it is formed. The cavity is concave from above downward, 

 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, and is slightly concave transversely ; the external por- 

 tion is convex above, slightly concave below. The articular surface, in the recent 

 state, is covered with a thin layer of cartilage. 



The Lesser Sigmoid Cavity is a narrow, oblong, articular depression, placed on 

 the outer side of tke coronoid process, and receives the lateral articular surface of 

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

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

 recent state it is covered with a thin layer of cartilage. 



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

 forward and from without inward, so as to be convex behind and externally ; its 

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

 outward ; it tapers gradually from above downward, and presents for examination 

 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 : its lower fourth, marked off from the rest of the 

 border by the commencement of an oblique ridge on the anterior surface, serves 

 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 subcuta- 

 neous 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 the 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 or interosseous border commences above by the union of two lines, 

 which converge one from each extremity of the lesser sigmoid cavity, enclosing 

 >etween them a triangular space for the attachment of part of the Supinator brevis. 



