Vol. 6$.~] 



CERVICAL VERTEBRA OP A ZEUGLODOX. 



125 



be mentioned that, in Protocetas atavus, Fraas, from the Mokattam 

 Limestones of Cairo and the oldest member of the Zeuglodontidae 

 yet known, the length of the centrum of the sixth cervical is much 

 greater in proportion to the height, being about as 2 to 3, showing 

 an approximation in the cervical vertebrae to the more normal mam- 

 malian type. The floor of the neural canal (n.c.) is convex from side 

 to side, and there is a blunt median ridge, on either side of which is 



Posterior surface of the cervical vertebra of Zeuglodon 

 Wanklyni, two-thirds of the natural size. 



v.c 



n.sp. == neural spine. 

 a.z. = anterior zygapophysis. 

 p.z. = posterior zygapophysis. 

 n.c. = neural canal. 



,c. = vertebrarterial canal. 

 p. = parapophysial process. 

 d. = diapophysial projection. 



a vascular foramen opening into the body of the centrum. On the 

 ventral surface of the centrum there is a faintly marked hypapo- 

 physial ridge. The neural arch is wide and high, the canal (n.c.) 

 being very large ; the pedicles of the arch are stout, and the zyg- 

 apophyses (a.z., p.z.) large and oval in outline ; there is a low neural 

 spine, but its precise height cannot be determined. The diapophyses 

 and parapophyses unite to form a broad, nearly vertical wing of 



