in.] DIVISION INTO REGIONS. 29 



body of the vertebra, the latter to its transverse process : 

 and that the former (capitular) attachment corresponds to 

 the interspace between the vertebrae, the head of the rib 

 commonly articulating partly with the hinder edge of the 

 body of the vertebra antecedent to that which bears its 

 tubercle. Hence the body of the last cervical vertebra 

 usually supports part of the head of the first rib. In the 

 posterior part of the series the capitular and tubercular 

 attachments commonly coalesce, and the rib is attached 

 solely to its corresponding vertebra. 



3. The Lumbar region consists of those vertebrae of the 

 trunk in front of the sacrum (to be afterwards denned) which 

 bear no movable ribs. It may happen that as the ribs 

 decrease in size posteriorly, the last being sometimes more 

 or less rudimentary, the step from the thoracic to the 

 lumbar region may be gradual and rather undetermined in 

 a given species. But most commonly this is not the case, 

 and the distinction is as well defined here as in any other 



region. 



As a general rule there is a certain relation between the 

 number of the thoracic and the lumbar vertebrae, the whole 

 number being tolerably constant in a given group of 

 animals, and any increase of the one being at the expense of 

 the other. Thus in almost all Artiodactyle Ungulata there 

 are 19 thoracico-lumbar vertebrae; but these may consist of 

 12 thoracic and 7 lumbar, or 13 thoracic and 6 lumbar, or 

 14 thoracic and 5 lumbar. 



The smallest number of thoracico-lumbar vertebrae in 

 Mammals occurs in some Armadillos, which have but 14. 

 The number found in Man, the higher Apes, and most Bats, 

 viz. 17, is exceptionally low ; 19 prevails in the Artiodactyles, 

 nearly all Marsupials, and very many Rodents; 20 or 21 in 



