V 







VERTEBRATED ANIMALS. 



These are the six parts which comparative anatomists con- 

 sider the elements of the vertebrae, and which are found in 

 most vertebrated animals, however various in form, size, 

 or habits, they may be. In some cases, however, in addi- 

 tion to these, there is the process f, bifid at the base, and 

 forming a spine at the lower surface of the vertebrae, 

 or opposite to the spinous process. This structure is 

 common in the fishes. The aperUr~ forced by the 

 bifurcation of this process, admits the passage of a large 

 artery. 



245. As our plan will not allow an extension of this 

 part of our subject to the different orders of the veile- 

 brata, we will omit any illustration from the quadrupeds, 

 as being most nearly allied to man in the scale of organi- 

 zation, and therefore most likely to present similar spines ; 

 and since illustrations the ntost remote from man in 

 the scale of being, will tend most clearly to show a 

 unity of plan in the construction of the whole, we will give 

 examples from some of the lower orders of vertebrated 

 animals. 



246. Vertebra of Fish. Fig. 67 represents a section 

 of a part of the spine of a fish Fj 67 

 standing in the natural position. 



The foody of each vertebra is 

 hollowed out on both sides so as 

 to form cup-like cavities; by 

 which means when the two con- 

 vex cavities are applied to each 

 other as in the living animal, 

 a cavity having the shape of a 

 short double cone is formed, as 

 shown in the figure. These cav- 

 ities left by the bones, are filled with a gelatinous substance 

 which is nearly incompressible, and which appears to 

 serve as a kind of pivot for the motions of the joint. By 

 dividing a spine in the centre, these parts are seen as 

 shown in the figure. 



247. A single vertebra is represented by Fig. 68, for the 



Explain Fig. 67. What is the difference between the vertebrae of quad- 

 rupeds and fishes ? 



