■so 



BONES OF THE THOKAX- 



]3ut on each side of the column a considerable extension of the cavity is 

 produced by the backward direction of the posterior parts of the ribs, 

 and thus the weight of the body is thrown further back and is more 

 equally distributed round the vertebral column. At the same time 

 a Ijroad furrow is produced between the spines of the vertebra and 

 the angles of the ribs, in which are placed the erectores spince muscles. 

 Theintercostal spaces are eleven in number, somewhat wider al)ove 

 than below, and varying in width with the elevation or depression of 

 the ribs. 



OSSIFICATION OF THE RIBS AND STERNUM. 



' The ossification of the ribs begins in cartilage posteriorly about the eighth 

 week, and extends rapidly forwards, so as to reach the permanent cartilage about 



Fig. 25. Fig. 25. — One of the 



Middle Ribs about 

 eighteen or twen- 

 ty years op age. 



(R. QUAIN.) 



1, the principal 

 piece or body ; 2, the 

 epiphysis of the liead ; 

 3, that of the tuber- 

 cle. 



the fourth month. 

 Subperiosteal ossi- 

 fication contributes 

 largely to their sub- 

 sequent growth. After puberty the centres of two small epiphyses appear in 

 the cartilage of the head and tubercle. These become united with the main bone 

 before the twenty-fifth year. 

 The ossification of the sternum begins about the sixth mouth, and usually by 



t3 



Fig. 2G. — Ossification of the STERNrsi. (R. Quain.) 



A, the cai-tilaginous stermnn before the middle of fcetal life. 



B, the stenuim of a chikl at birth. 1, 2, 3, & 4, luark the commencing ossific nuclei 

 For the manubrium and three upper pieces of the body. 



C, the sternum soon after puberty, sliowing cartihage between the manubrium and 



