20 THE VERTEBRAL COLUMN. [CHAP' 



(Fig. , //), 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 

 the last-named animal and the caudal vertebrae of many others. 

 This is termed a hypapophysis. Most commonly there is not . 

 even a trace of any such process. 



3. From the sides of the lower part of the arch, or from 

 the body, lateral processes project more or less directly out- 

 wards. These are called transverse processes. There may be 

 but one, or there may be two, superior and inferior, on each 

 side of a vertebra. In the latter case the superior is some- 

 times called a diapophysis, and the inferior a parapophysis : 

 though it is questionable whether the processes to which 

 these terms have been applied can always be regarded as 

 strictly homologous. 



(12.- 



FIG. 4. Side view of first lumbar vertebra of Dog (Canis familiaris), f. s spinous 

 process ; az anterior zygapophysis ; pz posterior zygapophysis ; in metapophysis ; 

 a anapophysis ; t transverse process. 



4. Besides these principal laterally projecting processes, 

 there are often others arising from the side of the arch, more 

 especially developed in the lumbar region, though by no 

 means constant even there. Of these there may be one or 

 two on each side. They have often been called accessory 



