852 



SKELETON 



The Second Cervical, known as the Axis or Epistropheus, as being 

 the pivot on which the Atlas and Head turn, is composed of seven 

 separate elements, the first of which is really the centrum of the 

 Atlas, but fused with the second, the centrum of the Axis, so as to 

 form the " odontoid process." The thinl and fourth are the pair of 

 pieces which form the neural arcli, and generally bear a prominent 

 spinous process. The fifth and sixth are a pair of rib-elements, each 

 of which is perforated by a transverse arterial foramen, and fuses with 

 the antero-lateral portion of the centrum and neural arch. The 

 seventh element is a single median piece wedged ventrally between 

 the anterior end of the axial centrum and the Odontoid process, 

 and is really equivalent to the second pair of basiventral elements, 

 having formed in the embryo the intervertebral pad connecting the 

 Odontoid with the body of the Axis, which last frequently carries on 

 its ventral side a single hypapophysis. The neural arch of the Axis 



Bx 



DiA.GRiVii OF First Three Cervical Vertebrae Diagram of Atlas from 



FROM THE LEFT SIDE. THE FRONT. 



C. Centrum ; C.i, Odontoid process ; B. Basiventral element ; B.i, tlie ventral half of tlie Atlas 

 ring ; /;.o, tlie first so-called Intercentrum ; /-'.y, the meniscus of Vertebra 3 ; Ch. Chorda 

 dorsaiis ; M. spinal canal ; I.t. Ligamentum trausversum ; N. Neural arcli. 



possesses a pair of postzygapophyses to articulate with the prse- 

 zygapophyses of the Third Vertebra, but owing to the reduced con- 

 dition of the Atlas the prsezygapophyses of the Axis are insignificant 

 or aborted, and in most of the Bucerotidm the Atlas is fused Avith 

 the Axis. In general the Axis, which owing to the Odontoid 

 process is really the compound of a vertebra and a half, is consider- 

 ably longer and larger than any one of 



The next succeeding Cenical Vertehrx, which have many features- 

 in common. Each of them consists of a centrum, a right and left 

 basidorsal piece, forming a neural arch above the spinal cord and 

 frequently sending out a long single or short bifurcated spinous 

 process, a pair of ribs and an intervertebral pad ; but the ribs have 

 mostly lost their shaft and are fused by their head and tubercle 

 with corresponding short knobs of the centrum or with larger 

 processes of the neural arch. A transverse foramen is alwa3'^s; 

 present, and is a rather characteristic feature. The centra frequently 



