VERTEBRAL COLUMN 



51 



Fig. 39a. — Diagram showing mode or Ossi- 

 fication OF Human Axis. (Ventral 

 surface. ) From Flower's Osteology of the 

 Mammalia. 



o, odontoid process, or centrum of atlas ; t, 

 proper centrum of axis ; na, neural arch ; 

 an, anterior articular surface ; c, e, e, e, epi- 

 physes, completing the ends of the centra, 



The transverse processes are simple in all but the cervical 

 region and arise from the base of the arch : in the thoracic region 

 they are tipped with cartilage on the ventral side of their distal 

 ends for articulation with the tubercle of the rib (p. 58). In the 

 lumbar and sacral regions 

 they arise from the centra, 

 and contain fused rib-ele- 

 ments. 



In loiig-neoked Ungulates 

 {e.g. Horse, Camel, Ox) the 

 neural spines of the anterior 

 thoracic vertebrae are greatly- 

 developed, and a correspond- 

 ingly strong cervical ligament 

 (ligamentum nuchse) is par- 

 ticularly well developed to 

 support the weight of the 

 head. This is also true of 

 antler-bearing animals and of 

 the Gorilla. 



The number of thoraco- 

 lumbar vertebrae varies greatly 

 in different Mammals : there 

 may be as few as fourteen 

 (Armadillo) or as many as 

 thirty (Hyrax). In Ungulates 

 the number is constantly 

 nineteen. In the lumbar ver- 

 tebrae the transverse pro- 

 cesses are especially long, 

 and other processes (anapo- 

 physes, metapophyses, hypa- 

 pophyses) are characteristi- 

 cally present in this region. 



Thus, as in Amphib- 

 ians, Reptiles and Birds, 

 the pelvis is connected 

 with the sacrum by means 

 of rudimentary ribs. As 

 iu the two last-mentioned 

 groups, there are not more 

 than two primary sacral 

 vertebrae, but except in 

 rnithorhynchus an d most 

 Marsupials a few caudal 

 become later included in 

 the sacrum and are usually 

 more or less closely united 

 with it by synostosis. The various processes of the sacral vertebrae 

 are more or less reduced. In Anthropoids, as in Man, the first 

 sacral vertebra is plainly marked off from the last lumbar by the 

 formation of the so-called nromontorii. A sacrum is wanting in 



E 2 



Fig. 39b. — Side View of the Twelfth 

 AND Thirteenth Thoraio Vertebr.e 

 OF Great Anteater (Myrmecophaija 

 juhafa), |. From Flower's Osteology of 

 the MammaUa. 



m, metapophysis ; ic, facet for articulation of 

 tubercle of rib ; cr, ditto for capitulum 

 of rib ; az, anterior zygapophysis ; as', 

 additional anterior articular facet ; pz. 

 posterior zygapophysis ; pz^ and j>;-, addi- 

 tional posterior articular facets. 



