H THE VERTEBRAL COLUMN. [chap. 



be thrown on the subject ; but at present it does not appear 

 that there is that uniformity in the plan of construction of 

 all vertebrae which has often been supposed, and definitions 

 of the different parts applicable in every case have not yet 

 been arrived at, and it may even be doubted whether this 

 will ever be possible. 



The principal processes commonly met with are as follow:— 

 i. From the middle of the upper part of the arch a 

 process generally single, but sometimes bifid at the end, 

 grows out vertically. This is the spinous process, or neural 

 spine already mentioned ; about its homology in different 

 vertebrae there never can be any question. It may however 

 be completely absent, when the arch is round or smooth 

 above, as in the cervical region in some animals ; on the 

 other hand, it may grow out into a very long conspicuous 

 rod of bone, as in the anterior dorsal region of others. 



2. Occasionally a process grows in the median line from 

 the under-surface of the body. This maybe single and long 



Fig. 3.— Anterior surface of the lumbar vertebra of Hare (Lepus timidus). s spinous 

 process ; m metapophysis ; az anterior zygapophysis ; / transverse process ; h 

 hypapophysis. 



iand slender, as in the anterior lumbar vertebrae of the Hare 

 (Fig. 3, h), or a sharp median ridge, as in the cervical verte- 

 brae of many Ungulata and the cervical and caudal vertebrae 

 of the Ornithorhynchus, or double, as in the atlas vertebra of 



