96 



BONES OF THE rPPER LIMB. 



nucleus for the body appears a little behind the glenoid cavity about the 7th or 

 8th week. Around this centre is fonned a triangular jtlate of bone, from near 

 the upper margin of which about the 3rd month the spine ajipears as a slight 

 ridge. At bu-th the coracoid and acromion process, the base and inferior angle, 

 the edges of the spine and of the glenoid cavity are cartilaginous. The nucleus 

 of the coracoid process is especially worthy of attention, both because it appears 

 in the first year, while the other siipplementai-y nuclei are formed only after pu- 

 berty, and because, although reduced to a mere epiphj-sis in mammals, it fonns a 

 distract and sometimes large bone in other vertebrate animals. The coracoid 

 process is united to the body about the age of puberty. The acromion process is 

 cartilaginous till the Hth or IGth year, when two distinct niiclei appear. These 

 soon coalesce and form an epiphysis which is united to the spme from the 22nd 

 to the 25th year. The cartilage of the base, which it may be noticed conesponds 



FiiT. S2. 



Fig. 82. — PosTERioPw Aspect of the Sternum and Right Shottlder Girdle from 

 A FcETus OF ABOUT FOUR MONTHS (Flower after Parker). Ih 



The dotted parts are cartilaginous ; ost, omosternum, afterwards becoming the inter- 

 articular fibro-cartilage ; pc, precoracoid of Parker ; a, acromion ; d, shaft of clavicle ; 

 •mss, mesoscapular segment of Parker ; c, coracoid ; rjc, glenoid cavity ; ijb, glenoid border ; 

 cb, coracoid border ; af, anterior or supraspinous fossa ; j)/, posterior or infraspinous 

 fossa ; ss, suprascapular border. 



to a more largely developed permanent cartilage or bone found in many animals, 

 becomes the seat of ossification about the 1 (Jth to the 1 Sth year, by the appear- 

 ance of a nucleus at the inferior angle, and thereafter of a line of osseous 

 deposit extendhig upwards throughout its length. The epiphysis thus fonned, 

 together with an epiphysial lamina which occasionally forms the border of the 

 glenoid cavity, are united to the body about the 25th year. 



Fig. 83. 



C..,.)A 



Fig. 83. — Ossification of the Clavicle 

 (R. Quain). 



a, the clavicle of a foetus at birth, osseous in 

 the shaft, 1, and cai-tilaginovis at both ends. 



b, cla-vicle of a man of about twenty-three 

 years of age ; the shaft, 1, fully ossified to the 

 acromial end ; tlie sternal epiphysis, 2, is repre- 

 sented rather thicker than natural. 



The clavicle begins to ossify before any other bone in the body. Its ossifica- 

 tion commences before the deposition of caitilage in connection with it, but 

 afterwards progresses in cartilage as well as in fibrous substance. It is foimed 



