THE SKELETON 



for the muscles by which we are enabled to bend the back and 

 to move those bones that articulate with the vertebral column. 



Between the bodies of the vertebrae are pads of elastic cartilage 

 or gristle called intervertebral cartilages. These unite the 

 vertebras, and form with them a flexible column. In old age the 

 cartilages of the backbone become hard and less flexible, so that 

 the back can no longer be bent, except to a very slight extent. 



The points in which these vertebrae differ from each other may receive a 

 passing notice. The bodies of the vertebrse increase in size from the first 

 cervical to the lowest lumbar, so 

 as to be able to support the greater 

 weight they have to bear. The 

 bodies of the cervical vertebra: 

 being small, we have seven joints 

 in a short column of bones. This 

 gives great freedom of motion to 

 the head and neck. The first 

 two cervical vertebrse will be 

 specially described in our next 

 lesson. The long spinous pro- 

 cesses of the dorsal vertebra, which 

 show so plainly in the backs of 

 thin persons, and the large spinous 

 and lateral processes of the lumbar 

 vertebrse, serve for the attach- 

 ment of the powerful muscles by 

 which we are enabled to bend the 

 body. The dorsal vertebras are 

 also provided each with two facets, 

 sometimes called the articular pro- Fig. 14. First .Dorsal Vertebra, with 



the first pair of Bibs, and a portion of 



the Sternum. 



cesses, with which the heads of the 

 ribs form movable joints. 



T,. , -11 _ !, .u_4. i, body of the vertebra; 2, spinal cavity ; 3, spinous 



It Will HOW be Seen that 'process: 4 , lateral processes; 5, articular facet 



a number Of these Vertebras, ^teral process ; 6, articular facet for the head 



, . , .,, ofthenb. (These two facets form, with the rib, 



arranged in a COlumn, Will movable joints.) 7, ribs ; 8, cartilage or gristle 



not Only form a powerful and connecting the ribs with the sternum ; 9, sternum, 



n ., , J r , , or breast-bone. 



flexible support, but that the 



vertebral arches will form a long bony tube. This tube is called 



the spinal canal, and contains the great nerve known as the spinal 



cord, to which the bones of the vertebral column serve as a strong 



protection. 



The ribs or costae, twenty-four in number, are curved bones, 

 connected in pairs with the dorsal vertebrae behind, and, except 

 the last two pairs, with the sternum (Gr. sternon, the breast) or 

 breast-bone in front. Each pair of ribs thus forms a circular arch 

 called a costal arch (fig. 14). That portion of the rib which forms 

 a movable joint with the articular process of the dorsal vertebrse 

 is termed its head. The other end is in most cases attached by 



