A STUDY OF THE SKELETON 



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ton are four bones, which in the adult become united in 

 one. From a fancied resemblance to a cuckoo's bill, this 

 part of the spinal column is called the coc'cyx (from Greek, 

 meaning cuckoo). Hence, in the spinal column of a child 

 there are thirty-three separate bones; in that of an adult, 

 twenty-six including sacrum and coccyx. 



The Structure of a Vertebra. The vertebrae are among 

 the most irregular bones of the body. In general one may 

 say that each consists of two parts ; namely, a mass of bone 

 called the cen'trum or body, and a bony arch with seven irregu- 

 lar processes. To 

 this region of the 

 vertebra is given 

 the name neu'ral 

 arch) because it 

 helps to inclose 

 the neural or spinal 

 cord. The centrum 

 is on the ventral 

 side of the spinal 

 column ; circular 

 in outline, it is flat- 

 tened above and 

 below, and on these surfaces are pads of cartilage that allow 

 the vertebrae, to a certain extent, to turn and bend on each 

 other. The weight of the body is supported by the body 

 of the vertebra. 



From the neural arch, as already stated, project seven 

 processes. One of these is the spi'nous process, which can 

 be felt in the middle of the back. It is this succession of 

 processes that has suggested the name spinal column. Two 

 lateral processes extend from the side of the neural arch, and 

 to these processes the ribs are attached in the dorsal region 

 of the spinal column. The other four projections from the 

 arch of the vertebra are called ar-tic'u-lar processes ; two of 

 them face dorsally, the other two ventrally. Since they 



FIG. 66. Parts of a Vertebra. 



A = side view. ar = articular process. 



B = top view. 6 = body or centrum. 



n = neural ring (containing spinal cord) . 

 sp = spinous process. tr transverse process. 



