CRANIUM. 399 



geons, since it provides for the flexibility of the 

 tail, and qualifies it for being applied to a great 

 variety of useful purposes, as we find more espe- 

 cially exemplified in the Ateles, or spider monkey, 

 and in the Kanguroo. 



Next in importance to the spine is the cra- 

 nium, or osseous covering of the brain ; together 

 with the bones of the face, which protect the 

 organs of the finer senses. An accurate investi- 

 gation of the mode in which these bones are 

 formed ho3 led many modern anatomists to the 

 opinion that they were originally parts of the 

 spinal column, and that they are in fact deve- 

 lopements of vertebrae, much altered, indeed, in 

 shape, in consequence of the new conditions to 

 which they have been subjected ; but still pos- 

 sessing all the essential elements of vertebrae. 

 In the embryo condition of these organs, and 

 while the brain is yet undeveloped, the resem- 

 blance of the bony circles which enclose it to 

 vertebrae is certainly very striking ; but in pro- 

 portion as the brain becomes expanded, the si- 

 milarity diminishes ; for the rapid growth of the 

 brain in the higher orders of animals is neces- 

 sarily attended with an equally sudden expan- 

 sion of the bones of the skull. Hence their 

 several elements are thrown into unusual posi- 

 tions, and being variously distorted and disfi- 

 gured, can hardly be recognised under the 

 strange disguises they assume. 



