PROTECTION, SUPPORT AND MOVEMENT 



509 



tary ribs, which are present in the other regions during embryonic 

 development, fuse onto the transverse processes. The first two cer- 

 vical vertebrae are modified to permit a free movement of the head. 

 The first, known as the atlas, has a pair of facets for articulating with 

 the pair of occipital condyles, the rounded bumps on the base of the 

 skull on each side of the foramen magnum. The head can rock back 

 and forth at this point. Tinning motion occurs at a unique joint be- 

 tween the atlas and the second cervical vertebra, the axis. All tetra- 

 pods have an atlas, but an axis does not appear in the evolutionary 



Zygomatic 



Cla.vicle 



Cnra-r-oid. /.(^ 

 process M7^\ 



Scapula 

 Humerus t 



OrBit 

 Exte.rna.1 narcs 



Cervical 



vertebra. 



Sternura 



•Thora.cic 

 vertebra. 



Lumbar 

 vertebra. 



Ilium. 



Sa.crum 



S ^^J^'.S W\ Co ccy3c 



Cajrpals 



Met a 



Pubis 

 Ischium, 



Tarsals 



■Metatarsals 

 Phalanges 



Figure 25.5. A ventral view of the human skeleton. 



