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A MANUAL OF ANATOMY 



Articulations. — Superiorly with the scapula, and inferiorly with 

 the radius externally, and ulna internally. 



Structure. — ^The shaft is composed of compact bone, which is 

 thicker at the centre than at the extremities. It contains a medul- 

 lary canal lined with a thin coating of cancellated tissue. The 

 articular extremities are filled with cancellated tissue, except at the 

 surface, where there is a thin layer of compact bone. 



Varieties. — These are (i) a supracondylar process, and (2) a supratrochlear 

 foramen. 



Ossification. — The humerus ossifies in cartilage from one primary, and seven 

 secondary, centres. The primary centre appears at the middle of the shaft 

 in the eighth week of intra-uterine life. At birth the shaft is ossified, but the 



Appears in the ist Year 



(^--•A.. Appears in the 3rd Year 

 Appears in the 5th Year 



All three coalesce at the 

 6th Year, and join at 20 



i^- 



. Appears at the 8th Week 

 (intra-uterine) 



Appears in the 14th Year 



—Appears in the 5th Year, 

 and joins at 18 



Appears in the 3rd Year Appears in the 12th Yeai 



The External Epicondyle, Capitellum, and Trochlea, 

 having previously coalesced, join at 17 



Fig. 106. — Ossification of the Humerus. 



extremities are cartilaginous. The superior extremity is ossified from three 

 secondary centres. The centre for the head appears in the first year (some- 

 times just before birth), that for the great tuberosity in the third year, and 

 that for the small tuberosity in the fifth year. The upper epiphyses join to 

 form one compound epiphysis in the sixth year, and this unites with the shaft 

 in the twentieth year. The lower extremity is ossified from four secondary 

 centres, as follows: one for the capitellum and outer half of the trochlea 

 appearing in the third year ; one for the internal epicondyle in the fifth year ; 

 one for the inner half of the trochlea in the twelfth year ; and one for the 

 external epicondyle in the fourteenth year. The trochlea, capitellum, and 

 external epicondyle join to form one compound epiphysis, and this unites 

 with the shaft in the seventeenth year. The internal epicondyle unites with 

 the shaft, as an independent epiphysis, in the eighteenth year. 



The law of ossification applicable to long bones with an epiphysis 

 or epiphyses at either end is as follows : the epiphysis or epiphyses, 



