THE SKELETON 41 



in mammals by any part of the vertebra itself, but by certain 

 distinct bones placed more or less in apposition to it, namely the 

 ribs in the thoracic, and the " chevron bones " in the caudal region. 

 In most cases the arch of one vertebra is articulated with that of 

 the next by distinct surfaces with synovial joints, placed one on 

 each side, called "zygapophyses " (az,pz), but these are often entirely 

 wanting when flexibility is more needed than strength, as in the 

 greater part of the caudal region of long-tailed animals. In addition 

 to the body and the arch, there are certain projecting parts called 

 processes, chiefly serving for the attachment of the numerous 

 muscles which move the vertebral column. Of these two are single 

 and median, viz. the spinous process, neural spine, or neurapophysis 

 (s), arising from the middle of the upper part of the arch, and the 

 hypapophysis from the under surface of the body. The latter, how- 

 ever, is as frequently absent as the former is constant. The other 

 processes are paired and lateral. They are the transverse processes 

 (f), of which there may be two, an upper and a lower, in which case 

 the former :is called, in the language of Owen (to whom we are 

 indebted for the terminology of the parts of vertebrae in common 

 use), " diapophysis," and the latter " parapophysis." Other processes 

 less constantly present are called respectively " metapophyses " (m) 

 and " anapophyses " (a). 



The vertebral column is divided for convenience of description 

 into five regions the cervical, thoracic or dorsal, lumbar, sacral, and 

 caudal. This division is useful, especially as it is not entirely 

 arbitrary, and in most cases is capable of ready definition ; but at 

 the contiguous extremities of the regions the characters of the 

 vertebras of one are apt to blend into 

 those of the next region, either normally 

 or as peculiarities of individual skeletons. 



Cervical Vertebrae. The cervical region 

 constitutes the most anterior portion of 

 the column, or that which joins the 

 cranium. The vertebras which belong to 

 it are either entirely destitute of movable 

 ribs, or if they have any these are small, 

 and do not join the sternum. As a general 

 rule they have a considerable perforation 

 through the base of the transverse process 

 (the vertebrarterial canal, Fig. 11, v) ; or, . J- -f ne < 



\ . 1-1111 sixth cervical vertebra of Dog. 



as it is sometimes described, they have s> gpinous process; az, anterior 



tWO transverse processes, superior and zygapophysis ; t>, vertebrarterial 

 . /. i . i ,1 , canal ; t, transverse process ; t , its 



inferior, which meet at their extremities inferio y la meiia. 



to enclose a canal. This, however, rarely 



applies to the last vertebra of the region, in which only the upper 



transverse process is usually developed. The transverse process, 



