210 



OSTEOLOGY. 



OLECRANON 



Separate centres are developed in connexion with the epicondyles ; that for the lateral 

 appears about the twelfth year, and, rapidly coalescing with the centres for the capitulum 

 and trochlea, forms an epiphysis, which unites with the body about the sixteenth or 



seventeenth year. The centre for the medial epicondyle 

 appears about the fifth year ; it forms a separate epi- 

 physis, which unites with the body about eighteen or 

 nineteen. These two epiphyses at the distal end of 

 the bone are separated by a down-growth of the 

 shaft, which lies between the medial epicondyle and 

 the trochlea, and forms part of the base and medial 

 side of the latter process. 



/(JORONOID PROCESS ml , -,. 1 . . , , .. 



1 he epicondylic process when present is developed 

 from the diaphysis, and has been observed to be 

 already well ossified by the third year. (" Proc. Anat. 

 Soc." Journ. Anat. and Physiol. 1898.) 



"INCISURA SEMILUNARIS 



INCISURA 



RADIALIS 



-TUBEROSITY 



"BlCIPITAL HOLLOW 



The Ulna. 



-POSTERIOR BORDER 



-INTEROSSEOUS BORDER 



Of the two bones of the forearm, the ulna, 

 which is placed medially, is the longer. It con- 

 sists of a large proximal extremity supporting 

 the olecranon and the coronoid process ; a body 

 or shaft tapering distally; and a small rounded 

 distal end called the head. 



Proximal Extremity. The olecranon lies in 

 line with the body. Its dorsal surface, more or 

 less triangular in form, is smooth and subcutane- 

 ous and covered by a bursa. Its proximal aspect, 

 which forms with the posterior surface a nearly 

 rectangular projection the tip of the elbow 

 furnishes a surface for the insertion of the tendon 

 of the triceps brachii muscle, together with a 

 smooth area which is overlain by the same 

 tendon, but separated from it by a bursal sac. 

 To the volar (anterior) crescentic border of this 

 process are attached the fibres of the posterior part 

 of the capsule and a portion of the ulnar collateral 

 ligament of the elbow-joint. The volar (anterior" 

 surface is articular, and enters into the formation 

 of the semilunar notch. 



The processus coronoideus (coronoid pro'cess) if 

 a bracket-like process, which juts forwards froir 

 the volar and proximal part of the shaft, and if 

 fused with the olecranon proximally. By itfj 

 proximal surface it enters into the formation o:j 

 the semilunar notch, whilst its volar aspect : 

 which is separated from its proximal side by t\ 

 sharp irregular margin, slopes distally anc 

 dorsally to become confluent with the vola? 

 surface of the body. Of triangular shape, this . 

 area, which is rough and tubercular, terminate!! 

 inferiorly in an oval elevated tubercle (tuberositai 

 ulnae), into which the tendon of the brachiali \ 

 muscle is inserted. Of the lateral margins oi 

 the coronoid process, the medial is usually th< 

 better defined. Proximally, where it joins th< 

 proximal border, thereis generally a salient tubercle 

 to which one of the heads of origin of the flexor digi 

 torum sublimis muscle is attached, whilst distal to this point the medial bordel 

 furnishes origins for the Dronator teres, and occasionally for the flexor pollici 



-HEAD 



.ARTICULAR CIRCUM- 

 FERENCE FOR RADIUS 

 ^GROOVE FOR EXT. CARPI 



ULNARIS 



STYLOID PROCESS 



FIG. 202. THE RIGHT ULNA AS VIEWED 

 FROM THE LATERAL SIDE. 



