OSSIFICATION OF THE BONES OF THE UPPER LIMB. 



107 



permanent cartilage or bone, suprascapular, found in many animals, becomes the seat of 

 ossification about the 16th to the 18th year, by the appearance of a nucleus at the inferior 

 angle, and thereafter of a line of osseous deposit extending upwards throughout its length. A 



Fig. 117. POSTERIOR ASPECT OF THE STERNUM 



AND RIGHT SHOULDER-GIRDLE FROM A 

 FCETl'S OF ABOUT FOUR MONTHS. (Flower 



after Parker.) 1 



The dotted parts are cartilaginous; ost, 

 omosternum of Parker, lateral part of epi- 

 sternum of Gegenbaur, afterwards becoming 

 the interarticular fibro-cartilage ; pc, pre- 

 coracoid of Parker ; a, acromion ; cl, shaft 

 of clavicle ; mss, mesoscapular segment of 

 Parker ; c, coracoid ; gc, glenoid cavity ; gb, 

 glenoid border ; cb, coracoid border ; of, 

 anterior or supraspinous fossa ; pf, posterior 

 or infraspinous fossa ; ss, suprascapular 

 border. 



thin lamina, in two pieces, is also added along the upper surface of the coracoid process, and 

 another at the margin of the glenoid cavity. These epiphyses are united about the 25th year. 

 In the numerals a nucleus appears near the middle of the shaft in the 8th week. It 

 gradually extends, until at birth only the ends of the bone are cartilaginous. In the 1st 

 year the nucleus of the head appears, and during the 3rd year that for the great tuberosity. 



Fig. 118. OSSIFICATION OF THE HUMERUS. (R. Quahl.) 



A, from a full-grown foetus ; B, in the second year ; C, at three years ; D, at the f f:h year ; E, at 

 about the twelfth year ; F, at the age of puberty. 



1, the primary centre for the shaft ; 2, nucleus for the head ; 3, that for the great tuberosity ; 4, 

 for the capitellum and adjacent part of the trochlea ; 5, for the internal couclyle ; 6, for the inner part 

 of the trochlea ; 7, for the external condyle. In this and the following figures the more advanced 

 bones are shown on a smaller scale than the earlier ones. 



The lesser tuberosity is either ossified from a distinct nucleus which appears in the 5thyear, 

 or by extension of ossification from the great tuberosity. These nuclei join together about 

 the 6th year to form 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 first appearing 

 in the capitellum in the 3rd year. The nucleus of the internal condyle appears in the 5th 

 year, that of the trochlea in the llth or 12th year, and that of the external condyle in the 

 13th or 14th year. The nucleus of the internal condyle forms a distinct epiphysis which 

 unites with the shaft in the 18th year ; the other three nuclei coalesce to form an epiphysis, 

 which is united to the shaft in the 16th or 17th year. 



The radius is developed from a nucleus which appears in the middle of the shaft in the 8th 

 week, and from an epiphysial nucleus in each extremity which only appears some time after 



