1 8 RIBS AND STERNUM. SKULL. SUTURES. 



9. The Ribs and Breast-Bone (Fig. 5). The ribs are 

 twenty-four slender curved bones, twelve on each side 

 of the chest. Every rib is attached behind to a vertebra, 

 the top one to the first vertebra below the neck. In 

 front, each rib ends in two or three inches of cartilage. 

 The breast-bone or sternum, h, lies in front of the chest. 

 Attached to its sides are the cartilages of most of the 

 ribs. The two lowest ribs are not joined to the breast- 

 bone and are sometimes called the free QV floating ribs. 



10. The Skull (Fig. 6) is made up of twenty-nine bones 

 (see table, p. 22); those behind and above arranged to 

 form the brain-box; and those in front, to support the 

 face. 



The organs of four of our senses, viz., those of hear- 

 ing, sight, smell, and taste, are also protected by the 

 skull-bones. 



11. The Sutures. Except the lower jaw-bone, which is 

 attached to the rest of the skull by a joint, to let us open 

 and close our mouths, nearly all the skull-bones are very 

 firmly united. In most cases the union is by a dovetail- 

 ing, like that used by cabinet-makers. Each bone has 

 its edge notched and fits accurately to the edge of the 

 next. This sort of junction between bones is called a 

 suture. It is well seen in Fig. 6 between the bone Pr 

 and those in front of, behind, and below it. 



12. How the Brain is Protected. The dome-like form 



9. What is the number and form of the ribs ? How attached 

 behind? How do they end in front? How attached to the breast, 

 bone ? Floating ribs ? 



10. How many bones in the skull? Use of those behind and above ? 

 Those in front ? What other organs do they protect ? 



IT. How is the lower jaw-bone attached? Union of other skull- 

 bones ? 'What is a suture ? 



12. What is the advantage of the dome-like form of the skull? II- 



