S?1NE OF THE VERTEBRATA. 



85 



we should be led to suppose that the frame-work of our 

 own species had first been constructed, and that the cor- 

 responding parts of other animals had been varied from 

 this, only so far as their means of existence, habits, or the 

 element in which they were destined to live, made it abso- 

 lutely necessary. 



243. We have p 1 :eady stated that the spine is the main 

 column, or IDT,! substantial part of the skeleton of verte- 

 brated animals, and we have described and figured this 

 part as it exists in our own frames. We will now show 

 the unity of design which exists in the construction of the 

 animal kingdom, by comparing the spines of other animals, 

 with that belonging to the human frame. 



244. Mechanical elements in the Vertebra. The num- 

 ber of elements, or mechanical parts which enter into the 

 composition of the vertebrae of different animals is shown 

 by Fig. 66. This does not represent the precise form of 

 any vertebra, but is meant to com- 

 bine the elements of the corres- 

 ponding parts as existing in verte- 



brated animals generally. The 

 first part is the nucleus or body of 

 the vertebrae 6, which is present in 

 all the species. Next in import- 

 ance is the bony plates, or leaves, 

 as they are called, /, /, which pro- 

 ceed from the sides of the body, 

 and embrace the spinal marrow, 

 which runs through the aperture 

 between them as shown in the 

 figure. Another essential element 

 is the spinous process, s, which 

 unites the two plates, and thus 

 completes the superior arch, of 

 which it may be considered as the keystone for the pro- 

 tection of the spinal cord. Then come the two transverse 

 processes, t, t, which extend outward, toward the sides, 

 and with which the ribs, r, r, are generally connected. 



Fig. 66. 



Explain Fig. 66. Point out the parts that are essential to a vertebra. 

 8 



