28 



BONES OF THE THORAX. 



each side are united together at their anterior extremities in two longitudinal 

 strips of cartilage, which afterwards join together in the middle line to 

 form the sternum. 



Fig. 24. 



Fig. 24. OSSIFICATION OF THE STERNUM. 



A, the cartilaginous sternum before the middle of foetal life. 



B, the sternum of a child at birth. 1, 2, 3, & 4, mark the commencing ossific nuclei 

 for the manubrium and three upper pieces of the body. 



C, the sternum soon after puberty, showing cartilage between the manubrium and 

 body, and imperfect union of the first, second, and third pieces of the body, while the 

 third and fourth are united. 



D, shows an example of a sternum at birth with an unusual number of ossific 

 centres, six in the manubrium, 1', which is very uncommon ; two pairs in the lower 

 pieces of the body, 3' & 4', which is not unusual ; 2, the single centre of the first piece of 

 the body. 



E, exhibits an example of the perforated sternum which probably depends upon the 

 imperfect union of the pairs of ossific nuclei shown in D in the lower part of the body ; 

 this figure also shows two episternat bones or granules, * *. 



Ossification. Each of the ribs is ossified from one principal centre, and 

 possesses two small epiphyses, one belonging to the head, and, except in 

 the last two ribs, another belonging to the tubercle. 



The sternum is ossified in a number of separate pieces, one, at least, for 

 each segment ; the manubrium sometimes possesses two, placed one above 



Fig. 25. ONE OF THE 

 MIDDLE RIBS OF A 

 PERSON ABOUT EIGH- 

 TEEN OR TWENTY 

 YEARS OF AGE. 



Showing, at 1, the 

 principal piece or body; 

 2, the epiphysis of the 

 head ; 3, that of the 

 tubercle. 



the other, and has 

 been found with a 

 greaternumber. The 

 third, fourth, and 



fifth segments, as well as the ensiform portion, are frequently formed 

 each from two nuclei placed side by side, which may remain distinct for 



