198 



A MANUAL OF ANATOMY 



a slip of the flexor longus poUicis 

 sometimes arises. Behind the 

 flexor subHmis tubercle there is 

 a depressed surface which gives 

 origin to the highest fibres of 

 the flexor profundus digitorum. 

 The outer surface presents the 

 small sigmoid cavity. 



The great sigmoid cavity, which 

 articulates with the trochlea of 

 the humerus, when viewed from 

 the side, forms half a circle. 

 The upper half of the cavity is 

 formed by the anterior surface 

 of the olecranon process, and the 

 lower half by the upper surface 

 of the coronoid process. It is 

 constricted at the centre by a 

 notch at either side, which marks 

 the meeting of the olecranon 

 and coronoid processes, the inner 

 notch being bridged over by a 

 fibrous band with which the 

 middle part of the internal lateral 

 ligament blends. The cartilage 

 of the cavity is sometimes broken 

 up at this part by a narrow, rough, 

 transverse interval. Extending 

 from the beak of the olecranon 

 to the beak of the coronoid there 

 is a longitudinal elevation, which 

 divides the cavity into two lateral 

 halves, the inner being concave 

 from side to side, and the outer 

 convex. 



The small sigmoid cavity, which 

 is situated on the outer surface of 

 the coronoid process, is concave 

 from before backwards, and ar 

 ticulates with the inner aspect 

 of the head of the radius. Its 

 anterior and posterior margins 

 give attachment to the cornua of 

 the orbicular ligament. 



The upper extremity presents 

 several nutrient foramina for 

 branches of the anterior and 

 posterior ulnar recurrent and 

 interosseous recurrent arteries. 



Triceps 



._ Beak of Olecranon Process 



-Great Sigmoid Cavity 

 -For Olecranon. Bursa 



,Beak of Coronoid Process 



--Small Sigmoid Cavity 

 — Anconeus 



■ Supinator Radii Brevis 



Oblique I-ine 



Extensor Ossis Metacarpi PoUicis 



Posterior Border 



Extensor Longus PoUicis 



.,... External or Interosseous Border 



Extensor ludicis 



^For Sigmoid Cavity of Radiil* • 



> - "^Head . - 



\ Groove for Extensor Carpi Ulnaris ! 



" Styloid Process 



Fig. III.— The Right Ulna 

 (Posterior Surface). 



