STRUCTURE OF VERTEBRAE. 353 



developed to suit particular occasions. Thus in 

 Fishes, we see that one or two additional pieces (i) 

 are affixed to the ends of each spinous process. In 

 many cases, instead of being thus placed in a line 

 with these processes, they appear at a little dis- 

 tance, having, according to this theory, wandered 

 from their proper situations ; they are then found 

 between the spinous processes, and receive the 

 name of inierspinous hones. 



The spinous processes have a tendency, when 

 their developement proceeds, to divide into two 

 branches ; and this bifurcation frequently takes 

 place also in the interspinous bones. The trans- 

 verse processes, likewise, occasionally develope ac- 

 cessory pieces, as is found to be the case in some 

 reptiles ; but, in other instances, they undergo a 

 gradual change of position, as we follow them back- 

 wards along the spinal column, where they descend 

 towards the abdominal region. 



The flexibility of particular portions of the spinal 

 column is regulated by the size and form of its pro- 

 cesses. When these are much developed, they 

 necessarily obstruct the flexion of the vertebrae in 

 the directions in which they are situated : when 

 they are small, no such hinderance arises, and the 

 spine is free to move in all directions. Thus, when 

 we see the spinous processes much enlarged, while 

 the transverse processes are small, we may infer 

 that the spine is incapable of any bending in that 

 direction ; but that it has the power of free lateral 

 flexion. This is the condition of the spine of fishes, 

 where this latter kind of motion is the one princi- 

 pally wanted. In Dolphins and other Cetacea, on 

 the contrar}^ where the actions are required to be 



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