SPINE OF THE VEKTEBRATA. 81 



arch on which the spinous processes are Fi S- 64 - 

 situated. These are called the trans- 

 verse processes of the vertebrae. The 

 arch formed by the united bases of these 

 processes, and a groove in the body of 

 the vertebra?, form the canal through 

 which the spinal marrow passes. This 

 aperture through a single vertebra, is 

 obvious in the adjoining figure. When 

 all are united, they form a continuous canal with solid 

 walls, for the protection of that most important part of 

 the animal system next to the brain, the spinal marrow. 



230. The spine is the great central beam of the whole 

 fabric of the skeleton. To this part all the other bones 

 are connected by muscles and joints, the whole being thus 

 combined into a general frame-work. It is the common 

 axis of all the motions of the limbs, by furnishing fixed 

 points for the attachment of all the larger muscles. 



231. Nowhere has the mechanical art of the Great 

 Architect of Nature been more skilfully displayed than in 

 the construction of this part of our frames. Had the 

 spine been made of a single rigid piece, it would be lia- 

 ble to fracture by blows which it now withstands with 

 impunity; and besides, such a construction would have 

 deprived us of a great variety of motions, which are 

 now so important to us in the business and comforts of life. 



232. Between the bodies of each bone there is an elas- 

 tic cartilage, allowing of a little motion in all directions ; 

 and this slight flexure in each part, being multiplied 

 through the whole column, admits of sufficient motion for 

 all our purposes. 



233. In addition to the cartilaginous connection, the spi- 

 nal bones are bound together by strong ligaments and mus- 



What does the word spine mean ? Why is the back bone called spine ? 

 How many bones does the spine consist of? How are these bones divi- 

 ded, and what names are given to each division ? What is said of the 

 mechanical importance of the spine ? What very important part does 

 the spine protect ? Which is the spinous, and which the transverse pro. 

 cesses of the spine? What most important portion of the system is pro 

 tected by the spine? What is said of the importance of the spine, as 

 connected with the other parrs of the bony fabric ? What would have 

 been the consequences, had the spine been formed of a single :>'ece ? 

 How are the several pieces of the spine connected together ? 



