40 OSTEOLOGY. 



shaft aids the surgeon in the diagnosis of many of the injuries to which the joints 

 are liable ; for it not unfrequently happens that, on the application of severe force 

 to a joint, the epiphyses become separated from the shaft, and such injuries may 

 be mistaken for fracture. 



Growth of Bone. Increase in the length of a bone is provided for by the deve- 

 lopment of new bone in the cartilage at either end of the shaft (diaphysis); and in 

 the thickness, by the deposition of soft ossifying blastema in successive layers 

 upon the inner surface of the periosteum. 



The entire skeleton in an adult consists of 204 distinct bones. These are 



Vertebral column (sacrum and coccyx included) . 26 

 Cranium ......... 8 



Ossicula auditus ....... 6 



Face . . .14 



Os hyoides, sternum, and ribs . . . . .26 



Upper extremities 64 



Lower extremities 60 



In this enumeration, the patellae and other sesamoid bones, as well as the 

 "Wormian bones, are excluded, as are also the teeth, which differ from bone both 

 in structure, development, and mode of growth. 



THE SPINE. 



The Spine is a flexuous column, formed of a series of bones called Vertebrae. 



The Vertebras are thirty-three in number, exclusive of those which form the skull, 

 and have received the names cervical, dorsal, lumbar, sacral, and coccygtal, according 

 to the position which they occupy ; seven being found in the cervical region, twelve 

 in the dorsal, five in the lumbar, five in the sacral, and four in the coccygeal. 



This number is sometimes found increased by an additional segment in one 

 region, or the number may be diminished in one region, the deficiency being 

 supplied by an additional segment in another. These observations do not apply- 

 to the cervical portion of the spine, the number of segments forming which is 

 seldom increased or diminished. 



The Vertebras in the three uppermost regions of the spine are separate segments 

 throughout the whole of life ; but those found in the sacral and coccygeal regions are, 

 in the adult, firmly united, so as to form two bones five entering into the formation 

 of the upper bone or sacrum, and four into the terminal bone of the spine or coccyx. 



GENERAL CHARACTERS OF A VERTEBRA. 



Each vertebra consists of two essential parts, an anterior solid segment or 

 body, and a posterior segment, the arch. The arch is formed of two pedicles 

 and two larninas, supporting seven processes ; viz., four articular, two transverse, 

 and one spinous process. 



The Bodies of the vertebras are piled one upon the other, forming a strong 

 pillar, for the support of the cranium and trunk; the arches forming behind these 

 a hollow cylinder for the protection of the spinal cord. The different segments 

 are connected together by means of the articular processes, and the transverse 

 and spinous processes serve as -levers for the attachment of muscles which move 

 the different parts of the spine. Lastly, between each pair of vertebras apertures 

 exist through which the spinal nerves pass from the cord. Each of these con- 

 stituent parts must now be separately examined. 



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