82 



BONES OF THE UPPER LIMB. 



The superior extremity of the ulna presents for articulation with the 

 humerus a large articular surface, the great sigmoid cavity, which looks 

 forwards and is bounded in its posterior and upper part by the olecranon, a 

 thick process continued upwards from the shaft, and in its lower part by 

 the coronoid process, which projects forwards. The great sigmoid cavity is 

 concave from above downwards, with its inferior wall deeper than its superior, 

 and is convex from side to side, being traversed by a vertical ridge. The 

 part external to this ridge is broad and convex above, while the part internal 

 to the ridge is broad and concave below : a slight constriction, and some- 

 times a notch of division, occurs across the middle of the cavity. Continuous 



Fig. 73. 



Fig. 73. RIGHT ULNA FROM BEFORE. 



Fig. 74. RIGHT ULNA FROM BEHIND AND WITHOUT. ^ 



1, point or beak of the olecranon ; 2, tuberosity of 

 the olecranon ; 3, end of the coronoid process ; 4, 

 greater sigmoid articular surface, 4 points to the 

 upper division of this surface ; 5, lesser sigmoid 

 cavity, and below it the ridge for the supinator brevis 

 muecle ; 6, external border or interosseous ridge ; 7, 

 lower extremity or head ; 8, styloid process ; 9, 

 rough surface of insertion of the brachialis anticus 

 muscle on the front of the coronoid process ; below 

 10, the oblique line marking the attachment of the 

 pronator quadratus muscle; 11, triangular surface 

 for the anconeous muscle ; 12, tipper part of the 

 posterior border, to the right of which the depressions 

 for the long extensor muscles of the fingers occupy 

 the posterior surface. 



with the great is the small sigmoid cavity, 

 a small articular surface on the outer side 

 of the base of the coronoid process, slightly 

 concave from before backwards, and articula- 

 ting with the cylindrical part of the head of 

 the radius. The olecranon forms by its 

 anterior surface a part of the articular sur- 

 face of the great sigmoid cavity ; superiorly, 

 broad and uneven, it gives attachment to 

 the triceps extensor muscle, and posteriorly ifc 

 presents a subcutaneous surface which is 

 continuous with the posterior margin of the 

 shaft. Between its anterior and superior 

 surfaces is an acute projection which fits, in 

 extension of the elbow, into the olecranon fossa 

 of the humerus, and between the superior and 

 posterior surface is a rectangular prominence 

 which forms the point of the elbow. The coronoid process terminates in a 

 sharp ridge, the prominent anterior extremity of which is received during 

 flexion into the coronoid fossa of the humerus : its superior surface forms 

 part of the surface of the great sigmoid cavity ; the inferior surface rises 

 gradually from the anterior surface of the bone, and is covered by a large 

 triangular roughness which gives iDsertion to the brachialis anticus muscle. 



The body or shaft in the upper three-fourths of its extent is three-sided, 

 and presents a slight curve with the convexity backwards, but near the 

 lower extremity is slender, straight and cylindrical. The anterior surface 

 is grooved in the upper half, where the flexor profundus muscle takes origin ; 

 and at its lower end has an oblique line to which the pronator quadratus 



