CRANIUM. 399 



geous, 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 cm* 

 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 hc-3 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. 



