THE VERTEBRAL COLUMN. 9 



what variously applied by anatomists?, is most frequently employed to denote an 

 eminence bearing a flattened articular surface. 



The cavities and depressions of bones are very various. An aperture or perfo- 

 ration, when short, is named a foramen ; when continued some way as a passage 

 it is termed a canal or meatus. A nan-ow slit is named Vifusure, an open excava- 

 tion or hollow in one or in several bones together is termed afomi. Tliis term is 

 also sometimes applied to the socket of a joint, as in the r/lcnoid or shallower, 

 and the coti/loid or deeper form of joint cavity. Sinus and antrum are names 

 applied to considerable cavities in the interior of certain bones. Besides these, 

 various other terms are employed which do not requii-e explanation, such as notch, 

 (incism^a) (jroovc,furron-, (sulcus), .Sec. 



The number of bones in the skeleton varies at different periods of 

 life, some which are originally distinct becoming united together as the 

 process of ossification advances. The following is a statement of the 

 number usually reckoned as distinct in middle life : — 



Single bones. 



The vertebral column . .26 

 The skull .... 6 

 The hyoid bone ... 1 

 The ribs and sternum . . 1 



The upper limbs 



The lower limbs 



34 83 200 



Besides the bones included in the above enumeration, there exist like- 

 wise the small auditory ossicles, and various bones formed in tendons and 

 called sesamoid, such as the patella, and tliose of the thmub and great 

 toe, usually amounting to 8 pairs or 16 in all. 



I.— THE VERTEBRAL COLUMN". 



The vertebral column is composed of a series of bones called verte- 

 hrce, Avhich are united together, for the most part, by joints and elastic 

 substance in such a manner that, although the amount of motion 

 allowed between each pair is slight, the aggregate is sufficient to give 

 the column very considerable flexibility. The vertebrai are originally 

 thirty-three in number. Of these, the twenty-four upper remain 

 separate in the adult, retaining their mobility, and are hence called 

 moveable vertebra3. They are succeeded by five others, which rapidly 

 diminish in size from above downwards, and which are united into one 

 mass called the sacmm ; beyond the sacrum are four dwindled terminal 

 members of the series, which as age advances, likewise become more or 

 less united, and form the cocci/x. These sacral and coccygeal vertebrae 

 have thus been called the fixed or vnited vertebrse. 



General characters of the Vertebrae. — The general characters are 

 best seen in the vertebrae placed near the middle of the column, of 

 which the sixth dorsal vertebra, shown in Fig. 8, may serve as an 

 example. Each has more or less the form of a ring, and presents for 

 consideration a body, arch, and processes. 



The Jjodji or cenfrimi (Owen), is a short cylinder or disc, which forms 

 the anterior part of the vertebra. Its superior and inferior surfaces are 

 nearly flat. Its anterior aspect is convex from side to side, but slightly 

 concave from above downwards. Its posterior surface fbrms part of the 

 ring, and is slightly concave from side to side. These vertical surfaces 



