554 



ANATOMY OF VERTEBRATES. 



363 



base of the broad sacral wedge gradually decrease in size to the 

 third cervical. In regard to breadth, they decrease to the fourth 

 dorsal, then increase to the first dorsal, and again decrease to the 

 second cervical. A soft elastic cushion of ' intervertebral ' sub- 

 stance lies between the bodies of the vertebrae. The distribu- 

 tion and libration of the trunk, ^^ith the superadded weight of the 

 head and arms, are favoured by these gentle curves, and the 

 shock in leaping is broken and diffused by the numerous elastic 

 intervertebral joints. The expansion of the cranium behind, and 

 the shortening of the face in front, give a globe-like form to the 

 skull, which is poised by a pair of condyles, advanced to near the 

 middle of its base upon the cups of the atlas ; so that there is but 

 a slight tendency to incline forward when the balancing action of 

 the muscles ceases, as when the head nods during sleep in an 

 upright posture. The free or ' true ' vertebra3 are c 7, D 12, L 5. 

 The metapophysis becomes distinct in the eleventh and well- 

 developed in the twelfth dorsal, in which the anaj)ophyses are 

 recognisable, and the diapophyses reduced to tubercles without 

 an articular facet. The neural spines increase in length and 



inclination ' sacrad ' (downward in 

 Man, backward in brutes) from the 

 fourth to the twelfth dorsal, and in 

 length and direction ' dorsad ' from 

 the fourth dorsal to the last cervi- 

 cal : they all have tuberous termi- 

 nations. 



The dorsal series of twelve verte- 

 bra, with all their elements, consti- 

 tute the * thorax ' in anthropotomy, 

 fig. 363, the parts of the much deve- 

 loped hajmal arches, not anchylosed 

 like those of the neural arches ^\ith 

 the centrum, being reckoned as 

 distinct bones. The pleurapophyses 

 are termed ' costae ' or ribs, the 

 htemapophyses ' costal cartilages ' 

 being rarely ossified : as many of 

 the haemal spines as may be ossified 

 are called ' sternum.' The first and 

 largest, which longest retains its 

 individuality, is the ' manubrium,' 

 it receives the cartilages of the first pair, and part of 



Bones of humau thorax, cxxiii-. 



fig. 364, h 1 



those of the second pair of ribs. 



The four succeeding 



sternebers,' 



