III.] DIVISION INTO REGIONS. 21 



and has some characters by which it may be placed in the 

 category of rudimentary ribs. 



The transverse processes of the anterior hmibar vertebrae 

 of certain Mammals, as the Pig, are originally autogenous 

 elements, though coalescing very early with the rest of the 

 vertebrae. 



In the sacral region, the separate lateral ossifications which 

 connect the vertebral column with the ilium present many 

 characters allying them to ribs. (See Fig. 6.) 



Fig. 6. — Anterior surface of first sacral vertebra (human), showing mode of develop- 

 ment, na neural arch ; c centrum ; / distincc (pleura^ophysial) o.ssificatioa for 

 attachment of ilium. 



Finally, the transverse processes of the caudal vertebrae of 

 some animals (as the Manati and Beaver) are separately 

 developed, though it is doubtful whether this circumstance 

 alone is sufficient to entitle them to be considered as costai 

 elements. 



Division of Vertebral Column into Regions. — For con- 

 venience of description the whole vertebral column has 

 been divided into five regions, the cervical, thoracic^ lumbar, 

 sacral, and caudal. 



This division is useful, especially as it is not entirely 

 arbitrary, and in most cases is capable of ready definition, 



^ Generally called dorsal, but it would be better to reserve this term 

 in morphology as relating to the upper surface of the body and opposed 

 to ventral. 



