308 THE VEKTEBRATE SKELETON. 



feature being the shape of the articulating surfaces of the 

 centra, which are generally described as saddle-shaped. The 

 anterior surface is convex from above downward, and concave 

 from side to side, while the posterior and more prominent 

 surface is concave from above downwards and convex from 

 side to side. The neural arch is low, and is drawn out into a 

 slight blade-like neural spine. Its base is deeply notched on 

 both sides posteriorly for the exit of the spinal nerves. Above 

 these notches it is drawn out into two rather prominent 

 diverging processes, which bear the postzygapophyses, 

 two flattened surfaces which look downwards and outwards. 

 The transverse processes form irregular outgrowths from 

 the anterior two-thirds of the sides of the vertebra ; each 

 projects for a short distance downwards and outwards, and 

 is terminated posteriorly by a short backwardly-projecting 

 spine. The transverse processes are shown by development 

 to ossify from separate centres, and are therefore to be 

 regarded as cervical ribs, and each is perforated at its base by 

 a canal for the passage of the vertebral artery. Above the 

 anterior end of the vertebrarterial canal are a pair of 

 thickened outgrowths, which bear upwardly and inwardly 

 directed prezygapophyses. Each transverse process is 

 perforated near its middle by a prominent foramen through 

 which passes a vein which is connected with the jugular vein. 



The third and fourth cervical vertebrae resemble the suc- 

 ceeding ones in most respects, but have small hypapophyses, 

 and the neural spines are less blade-like. The posterior 

 cervical vertebrae (tenth to sixteenth) differ somewhat from 

 the middle ones. They are shorter and more massive, the 

 neural arch is much shorter, being deeply notched in the 

 middle line in front and behind. The transverse processes arise 

 from the anterior half of the vertebra only, and in the eleventh 

 vertebra each is drawn out below into a pair of rather promi- 

 nent downwardly and inwardly directed processes. In the 

 twelfth vertebra these processes have almost coalesced, and 





