THOEACIC LIMBS 559 



inner condyle, the pronator teres, the flexor carpi radialis, the 

 flexor profundus digitorum, the palmaris longus, and the flexor 

 carpi ulnaris ; on the posterior border and the external supracondyloid 

 ridge, the supinator longus, the extensores carpi radialis longior and 

 brevior and comrnunis digitorum ; on the outer condyle, the exten- 

 sores minimi digiti and carpi ulnaris and the supinator brevis. 



Blood Supply. The nutrient artery for the shaft of the humerus 

 arises from the brachial artery in the lower third of the arm, a little 

 above the supracondyloid foramen, often in common with a large 

 muscular branch for the biceps muscle. 



Ossification. The humerus is developed from seven centres of 

 ossification, namely, for the shaft, for the head and greater tuberosity, 

 for the capitellum, for the trochlea, for the inner condyle, for the outer 

 condyle, and for the lesser tuberosity. 



At birth the shaft is already ossified, and a small centre is visible 

 in the upper extremity. At thirty days the upper extremity is largely 

 ossified, and the lower extremity, which is still almost entirely cartilagi- 

 nous, exhibits a large centre for the capitellum and a small centre for 

 the trochlea. At forty-four days there is a centre of good size on the 

 back of the inner condyle, and a very small centre has appeared in the 

 outer part of the outer condyle. At sixty days the lesser tuberosity ex- 

 hibits a distinct centre. At one hundred and thirteen days the centre 

 in the outer condyle has coalesced with the capitellum, which has joined 

 the trochlea. 



VARIATIONS IN THE HUMERUS. 

 VARIATIONS IN SIZE. 



The measurements of the humerus are taken as follows : 



The maximum length is the distance on the long axis from the top 

 of the greater tuberosity to the most projecting point of the inner 

 edge of the lower articular eminence. 



The width at the upper end is the greatest transverse diameter 

 from tuberosity to tuberosity. 



The height at the upper end is the antero-posterior diameter from 

 the anterior border to the posterior most projecting point of the 

 articular surface of the head. 



The width at the condyles is the maximum transverse diameter. 



The height at the condyles is the greatest antero-posterior diameter 

 measured with sliding calipers. 



