OSSIFICATION OF THE HUMERUS. 



97 



from two separate centres, the one appearmg about the fith week, for the shaft 

 and acromial end, the other appearing about the 18th to the 2()th year for an epi- 

 physis at the sternal end. The epiphysis is united to the shaft about the 25th 

 year. 



In the humerus an ossific nucleus appears near the middle of the shaft in 

 the 8th week. It gradually extends, until at bu-th only the ends of the bone 

 are cartilaginous. About the beginning of the 2nd year the nucleus of the 

 head appears, and during the .3rd year that for the gi'eat tuberosity. The lesser 

 tuberosity is either ossified fi-om a distinct nucleus which appears in the .5th 

 year, or by extension of ossification fi-om the great tuberosity. These nuclei 

 unite together about the 5th year to fonn an epiphysis, which is not united to 

 the shaft till the 20th year. In the cartilage of the 'lower end of the bone four 

 separate nuclei are seen, the fii-st appearing in the capitellum in the 3rd year. 



Fig. 84. — Ossification of the Humerus (R. Quain). 



A, from a full grown foetus ; B, at two years ; C, in the thh'd year ; D, at the 

 beginning of tlie fifth year ; E, at about the twelfth year ; F, at tlie age of puberty. 



1, the primary centre for tlie shaft ; 2, nucleus for the articular head ; 3, that for the 

 great tuberosity ; 4, for the radial condyle and adjacent part of the trochlea ; 5, for the 

 inner or trochlear eminence ; 6, for the inner part of the trochlea ; 7, for the external 

 or capitellar eminence. In tliis and the following figures the more advanced bones are 

 shown on a smaller scale than the earlier ones. 



The nucleus of the internal condylar eminence appears in the 5th year, that of 

 the trochlea in the 11th or 12th year, and that of the external condylar eminence 

 in the 13th or 14th year. The nucleus of the internal condylar eminence forms 

 a distinct epiphysis which unites -R-ith the shaft in the 18th year: the other 

 three nuclei coalesce to form an epiphysis, which is united to the shaft in the 

 IGtli or 17th year. 



The radius is developed fi-om an osseous nucleus, which jrppears in the middle 

 of the shaft in the 8th week, and from an epiphysial nucleus in each ex- 

 tremity which only appear some time after birth. The nucleus in the caiiial 

 extremity appears at the end of the 2nd year, while that of the head is not 

 seen till the 5th or 6th year. The superior epiphysis and shaft unite about 

 the 17th or 18th year ; the inferior epiphysis and shaft unite about the 20th 

 year. 



The ulna is ossified similarly to the radius, but ossification begins a few days 

 later. The nucleus of the shaft appears about the 8th week, that of the carpal 



VOL, I. H 



3 



