HUMERUS. 



133 



Fig. 89. Plan of the Development of the 

 Humerus. By 7 Centres. 



EpipJiystsefHeadti\ A* 

 TubfrasMex //*/ <*^ ley 

 ' y'. r 



one for the greater tuberosity, one for the radial portion of the articular surface, 

 one for the trochlear portion, and one for each condyle. The centre for the shaft 

 appears very early, soon after ossification has commenced in the clavicle, and 

 soon extends towards the extremities. At birth, it is ossified nearly in its whole 

 length, the extremities remaining cartilaginous. Between the first and second 

 years, ossification commences in the head of the bone, and between the second 

 and third years the centre for the tuberosities makes its appearance usually by a 

 single ossific point, but sometimes, according to Beclard, by one for each tube- 

 rosity, that for the lesser being small, and not appearing until after the fourth 

 year. By the fifth year, the centres for the head and tuberosities have enlarged 

 and become joined, so as to form a single large epiphysis. 



The lower end of the humerus is devel- 

 oped in the following manner : At the end 

 of the second year, ossification commences 

 in the radial portion of the articular sur- 

 face, and from this point extends inwards, 

 so as to form the chief part of the articular 

 end of the bone, the centre for the inner 

 part of the articular surface not appearing 

 until about the age of twelve. Ossification 

 commences in the internal condyle about 

 the fifth year, and in the external one not 

 until between the thirteenth or fourteenth 

 year. About the sixteenth or seventeenth 

 year, the outer condyle and both portions 

 of the articulating surface, having already 

 joined, unite with the shaft ; at eighteen 

 years, the inner condyle becomes joined, 

 whilst the upper epiphysis, although the 

 first formed, is not united until about the 

 twentieth year. 



Articulations. "With the glenoid cavity 

 of the scapula, and with the ulna and radius. 



Attachment of Muscles. To the greater 

 tuberosity, the Supra-spinatus, Infra-spina- 

 tus, and Teres minor ; to the lesser tube- 

 rosity, the Subscapularis ; to the anterior 

 bicipital ridge, the Pectoralis major; to the 

 posterior bicipital ridge and groove, the 

 Latissimus dorsi and Teres major ; to the 

 shaft, the Deltoid, Coraco-brachialis, Bra- 

 chialis anticus, external and internal heads 



of the Triceps ; to the internal condyle, the Pronator radii teres, and common 

 tendon of the Flexor carpi radialis, Palmaris longus, Flexor digitorum sublimis, 

 and Flexor carpi ulnaris ; to the external condyloid ridge, the Supinator longus, 

 and Extensor carpi radialis longior ; to the external condyle, the common tendon 

 of the Extensor carpi radialis brevior, Extensor communis digitorum, Extensor 

 minimi digiti, and Extensor carpi ulnaris, the Anconeus, and Supinator brevis. 



THE FOREARM. 



The Forearm is that portion of the upper extremity, situated between the elbow 

 and wrist. It is composed of two bones, the Ulna, and the Radius. 



THE ULNA. 



The Ulna (figs. 90 and 91), so called from its forming the elbow (xswj), is a long 

 bone, prismatic in form, placed at the inner side of the forearm, parallel with the 



Unites iotth\ 

 Shaft at I. 



***3* M 



