170 ELEMENTS OP OENITHOLOGT. 



Various bony prominences projecting from the vertebra are 

 termed processes. 'From the middle of the dorsal side of the 

 neural arch there generally arises a prominence called the neural 

 spine or neurapophysig, though it is sometimes simply called the 

 spinov^ process. Prominences which jut out laterally from the 

 side of the neural arch or centrum are called transverse processes. 

 There may be two of them on either side. In such case the 

 superior one is called the dtapophysis or tubercular transverse 

 process, and the inferior one the parapophysis or capitular 

 transverse process. The distal ends of these two processes may 

 be connected on either side by an osseous bridge, which may 

 be prolonged into a process — the pleur apophysis. Two pro- 

 cesses may arise, one from either side of the ventral surface of 

 the centrum, and meeting together below form an arch beneath 

 it comparable with the " neural arch " above. Such an inferior 

 arch is termed a hernial arch, and serves to protect and transmit 

 blood-vessels. 



A median process may depend from the middle surface of 

 the centrum or the ventral end of the hsemal arch. Such a part 

 is named a hypapophysis, and it may bifurcate laterally, as in 

 the Penguins. 



Two other processes generally project forwards and two 

 backwards from the neural arch of each vertebra. These four 

 are termed zygapophyses or articular processes. They are so 

 termed because they serve to articulate adjacent vertebrae toge- 

 ther. Each articular surface of the anterior pair of zygapophyses, 

 or prezygapophyses, looks more or less dorsally, or dorsad, and 

 receives upon it the articular surface of one of the pair of 

 posterior zygapophyses, or postzygapophyses, the articular sur- 

 faces of which look more or less ventrally, or ventrad. 



Adjacent vertebrae are also articulated by the adjacent sur- 

 faces of their centra. Parts which thus articulate have inter- 

 posed between a membranous bag, or synovial membrane; so 

 called because it contains synovia, or joint-oil — an arrangement 

 which facilitates movement and diminishes friction. Adjacent 

 vertebrae may completely unite with each other or with other 

 parts of the skeleton. Such parts are then said to be anchylosed 

 together. 



The vertebrae are divisible into four categories : — (1) Those 

 of the neck, or cervical vertebrae ; (2) those of the trunk, or 

 dorsal vertebrae ; (3) those intermediate between these and the 



