THE SKELETON 



225 



tight onto the face of the vertebra above and also onto the face of the 

 vertebra below. By means of these disks a very close connection is 

 secured between the vertebrae on the front side of the column. 



b. On the back of the column, the downward projections from the 

 neural arch of each vertebra above fit into depressions found in the 

 neural arch of the vertebra below. This interlocking of the vertebras, 

 which is most marked in the lumbar region, strengthens greatly the 

 back portion of the column. 



c. To further secure one bone upon the other, numerous ligaments 

 pass from vertebra to vertebra on all sides of the column. 



2. The Skull. The skull is formed by the close union 

 of twenty-two irregular bones. These fall naturally into 

 two subgroups the cranium and the face (Fig. 100). The 

 cranium consists of eight 



thin, curved bones which 

 inclose the space, called 

 the cranial cavity, that 

 holds the brain. The 

 face group, consisting 

 of fourteen bones, pro- 

 vides cavities and sup- 

 ports for the different 

 organs of the face, and 

 supplies a movable part 

 (the inferior maxillary) FIG. 100. The skull (Huxley). The 



which, with the bones illustration shows most of the bones of the 



above (superior maxil- 



lary), forms the machine for masticating the food. 



3. The Thorax. This group contains twenty-four bones 

 of similar form, called ribs, and a straight flat bone, called 

 the sternum, or breastbone (Fig. 101). The ribs connect 

 with the spinal column behind, and all but the two lowest 

 ones connect with the sternum in front, and, by so doing, 

 inclose the thoracic cavity. As already stated (page 85), 



Lachr 

 mal 



