SPINE OF THE. VERTEBRATA. 



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

 own species had first been constructed, and that the 

 corresponding 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 absolutely necessary. 



We have already stated that the spine is the main 

 column, or most substantial part of the skeleton of ver- 

 tebrated 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 construc- 

 tion of the animal kingdom, by comparing the spines of 

 other animals with that belonging to the human frame. 



Mechanical elements in the Vertebra. The number 

 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 

 Fig. 66. form of any vertebra, but is 



meant to combine the elements 

 of the corresponding parts as 

 existing in vertebrated animals 

 generally. The first part is the 

 nucleus or body of the vertebra 

 &, which is present in all the 

 species. Next in importance is 

 the bony plates, or leaves as they 

 are called /, /, which proceed 

 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 ele- 

 ment is the spinous process s, 

 which unites the two plates, and 

 thus completes the superior arch, of which it may be 

 considered as the key-stone for the protection of the 

 spinal cord. Then come the two transverse processes 

 t, t, which extend outwards, towards the sides, and with 

 which the ribs r. r, are generally connected. These 



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

 8* 



