SKELETON 



849 



(6) Cervico-dorsal Vertebrae, with movable ribs which do not 

 reacli the sternum. Their number may vary from 1 to 5, often 

 individually and then in smaller limits. 



II. Dmsal Vertehrx begin at the first that is connected with the 

 sternum by a pair of complete ribs, and end at the last that is not 

 fused with the ilium. 



III. Pelvic Vertehrse are all those that are fused with the iliac 

 portion of the PELVIS, some of the anterior of them frequently 

 bearing long and often complete and movable ribs, occasionally 

 reaching the sternum. Hence it follows that " Thoracic " Vertebrse, 

 or those which are connected with the sternum, are not neces- 

 sarily Dorsal Vertebrae, and therefore unless clear definitions are 

 strictly adopted, a promiscuous application of those terms will lead 

 to much confusion. This remark applies with still greater force to 

 the terms " dorso-lumbar " and " lumbar " Vertebrse, which have 

 a well-defined meaning in Mammals and in most Reptiles ; but are 

 absolutely inapplicable to Birds, as will presently be seen (page 855).^ 



IV. Caudal Vertehrx, those following the last, and not connected 

 with the ilium. 



A typical Bird's vertebra consists of the centrum, an arch and 

 two ribs. Roughly speaking, the arch encloses the spinal cord, and 

 frequently extends dorsally into a spinous process, the size and 

 position of which vary considerably in the dift'erent regions of the 

 vertebral column. The arch also sends out a pair of anterior and 

 a pair of posterior oblique processes (commonly called praizyga- 

 pophyses and postzygapophyses), as well as a right and a left trans- 

 verse process. The oblique processes terminate in facets, which 

 articulate with those of the adjoining vertebra, so that the facets of 

 the prsezygapophyses look upwards and forwards and are overlapped 

 by those of the postzygapophyses of the vertebra next in front. 

 When the vertebrse ax-e free this rule is absolute, except in the case 



^ Table shewing the Numerical Diversity of the several 

 Vertebral Regions in some forms of Birds. 



54 



