66 THE HUMAN BODY. 



the face. Attached by ligaments to the under side of the 

 cranium is the Jiyoid lone, to which the root of the tongue is 

 fixed. 



Of the twenty-four separate vertebrae of the adult the seven 

 nearest the skull (Fig. 17, C 1-7) lie in the neck and are 

 known as the cervical vertebra. These are followed by 

 twelve others which have ribs attached to them (see Fig. 16) 

 and lie at the back of the chest; they are the thoracic or dorsal 

 vertebrae (D 1-12). The ribs (Fig. 28) are slender curved 

 bones attached by their dorsal ends, called their heads, to the 

 thoracic vertebrae and running thence round the sides of the 

 chest. In the ventral median line of the latter is the breast- 

 bone or sternum (d, Fig. 16). 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. 



The Thoracic or Dorsal Vertebras. If a single vertebra, 

 say the eleventh from the skull, be examined carefully it will 

 be found to consist of the following parts (Figs. 18 and 19) : 



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

 on each end where it is turned towards the vertebrae above and 

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

 of the vertebra, and the series of vertebral bodies (Fig. 17) 

 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 the neural 

 arch, A 9 which with the back of the body incloses a space, 

 Fv, the neural ring. In the tube formed by the rings of the 

 successive vertebrae lies the spinal cord. Projecting from the 

 dorsal side of the neural arch is a long bony bar, Ps, the 

 spinous process : and the projections of these processes from 

 the various vertebrae can be felt through the skin all down 

 the middle of the back. Hence the name of spinal column 

 often given to the whole back-bone. 



Six other processes arise from the arch of the vertebra: 

 two project forwards, i.e., towards the head; these, Pas, are 

 the anterior articular processes and have smooth surfaces, 

 covered with cartilage, on their dorsal sides. A pair of simi- 

 lar posterior articular processes, Pai, runs back from the 

 neural arch, and these have smooth surfaces on their ventral 

 aspects. In the natural position of the vertebra, the smooth 

 surfaces of its anterior articular processes fit upon the poste- 



