106 



ULNA. 



Fig. 51. 



depression on the head of the radius ; the internal portion 

 is a concave and pulley-like surface, trochlea, which arti- 

 culates with the ulna. Projecting beyond the articular 

 surface on each side are the external andinternal condyles, 

 the latter being considerably the longer ; and running up- 

 wards from the condyles upon the borders of the bone are 

 the condyloid ridges, of which the external is the most 

 prominent. Immediately in front of the trochlea is a 

 small depression for receiving the coronoid process of the 

 ulna during flexion of the fore-arm ; and immediately be- 

 hind it a large and deep fossa, for containing the olecra- 

 non process in extension. 



Development. By seven centres ; one for the shaft, one 

 for the head, one for the tuberosities, one for the eminen- 

 tia capitata, one for the trochlea, and one for each con- 

 dyle, the internal preceding the external. Ossification 

 commences in the diaphysis of the humerus soon after the 

 clavicle ; in the head and tuberosities, during the second 

 and third years of infantile life ; in the eminentia capitata 

 and trochlea during the third and sixth years ; and in the 

 condyles during the twelfth and fifteenth. The entire 

 bone is consolidated at twenty. 



Articulations. With the glenoid cavity of the sca- 

 pula, and with the ulna and radius. 



Attachment of Muscles. To twenty-four ; by the greater tuberosity to 

 the supra-spinatus, infra-spinatus, and teres minor ; lesser tuberosity, sub- 

 scapularis; anterior bicipital ridge, pectoralis major; posterior bicipital 

 ridge and groove, teres major and latissimus dorsi ; shaft, external and 

 internal heads of the triceps, deltoid, coraco-brachialis, and brachialis 

 anticus ; external condyloid ridge and condyle (condylus extensorius), 

 extensors and supinators of the fore-arm, viz. supinator longus, extensor 

 carpi radialis longior, extensor carpi radialis brevior, extensor communis 

 digitorum, extensor minimi digiti, extensor carpi ulnaris, anconeus, and 

 supinator brevis ; internal condyle (condylus ftexorius], flexors and one 

 pronator, viz. pronator radii teres, flexor carpi radialis, palmaris longus, 

 flexor sublimis digitorum, and flexor carpi ulnaris. 



ULNA. The ulna is a long bone, divisible into a shaft and two extre- 

 mities. The upper extremity is large, and forms principally the articula- 

 tion of the elbow ; while the lower extremity is small, and excluded from 

 the wrist-joint by an inter-articular nbro-cartilage. 



The superior extremity presents a semilunar concavity of large size, the 

 greater sigmoid notch, for articulation with the humerus ; and upon the 

 outer side a lesser sigmoid notch, which articulates with the head of the 

 radius. Bounding the greater sigmoid notch posteriorly is the olecrajion 

 process ; and overhanging it in front, a pointed eminence with a rough 



* The humerus of the right side ; its anterior surface. 1. The shaft of the bone. 2. 

 The head. 3 The anatomical neck. 4. The greater tuberosity. 5. The lesser tube- 

 rosliy. 6. Tne bicipital groove. 7. The anterior bicipital ridge. 8. The posterior 

 bicipieal ridge. 9. The rough surface into which the deltoid is inserted. 10. Trie nu- 

 tritious foramen. 11 The eminentia capitata. 12. The trochlea. 13. The external 

 condyle. 14. The internal condyle. 15. The external condyloid ridge. 16. The inter 

 nal condyioid ridge. 17. The fossa for the coronoid process of the ulna. 



