VERTEBRA. 65 



movable vertebrae, comes the sacrum (8 1), made up of 

 five vertebrae, which in the adult grow together to form 

 one bone, and below the sacrum is the coccyx (Co 1-4), 

 consisting of four very small tail vertebrae, which in ad- 

 vanced life also unite to form one bone. 



On the top of the vertebral column is borne the skull, 

 made up of two parts, viz., a great box above which in- 

 closes the brain and is called the cranium, and a large 

 number of bones on the ventral side of this which form the 

 skeleton of the face. Attached by ligaments to the under 

 side of the cranium is the hyoid bone, to which the root of 

 the tongue is fixed. 



Of the twenty-four separate vertebrae of the adult the 

 seven nearest the skull (Fig. 14, C 1-7) lie in the neck 

 and are known as the cervical vertebrce. These are fol- 

 lowed by twelve others which have ribs attached to them 

 (see Fig. 13) and lie at the back of the chest; they are the 

 dorsal vertebra (D 1-12). The ribs (Fig. 25 *) are slender 

 curved bones attached by their dorsal ends, called their 

 heads, to the dorsal vertebrae and running thence round the 

 Asides of the chest. In the ventral median line of the lat- 

 / ter is the breast-bone or siernum (d, Fig 13). Each rib 

 near its sternal end ceases to be bony and is composed of 

 cartilage. 



These parts skull, hyoid bone, vertebral column, ribs, 

 and sternum constitute the axial skeleton, and we have 

 now to consider its parts more in detail. 



The Dorsal Vertebrae. If a single vertebra, say the 

 eleventh from the skull, be examined carefully it will be 

 found to consist of the following parts (Figs. 15 and 16): 



First a bony mass, C, rounded on the sides and flattened 

 on each end where it is turned towards the vertebras above 

 and below it. This stout bony cylinder is the "body" or 

 centrum of the vertebra, and the series of vertebral bodies 

 (Fig. 14) forms in the trunk that bony partition between 

 the dorsal and ventral cavities of the body spoken of in 

 Chapter I. To the dorsal side of the body is attached an 

 arch (he neural arch, A, which with the back of the body 

 incloses a space, Fv, the neural ring. In the tube formed 



*P. 73. 



