218 



DESCRIPTION OF A SPECDIEN 



marked, and leave the under side of the bone to get on to the posterior corner of the end 

 of the transverse process. 



Articulating Processes [Zygrqwiohyses). [A in woodcuts.) — These are found in the 

 cervical and more or less plainly in the first five dorsal vertebrae. In the 3d cervical the 

 anterior zygapophysis is an oval, smooth surface placed on the outer end of the arch by 

 the origin of the diapophysis, having its long diameter transverse. In the succeeding 

 vertebrae it gradually changes its position so that the long diameter points forward 

 and outward. The surface begins to face inward with the first dorsal. In the 4th, this 

 surfiice is on the inner side of the metapophyses facing directly inward. In the 

 5th, it is largely perceptible. The posterior zygapophyses, more or less convex, follow the 

 variations of the anterior ones, though of course in an inverted direction. Those of the 

 anterior vertebrae face backward, those of the posterior outward. They of course get 

 nearer together. It is important to observe that the series of the zygapophyses is contin- 

 ued on to the anterior side of the arch of the axis and to the postei'ior side of the arch of 

 the atlas. The surfaces on the latter almost meet in the median line. The zygapophyses 

 are clearly continued towards the tail, as the projections at the base of the spinous process 

 already mentioned. 



The metapophyses (C in cut) are first seen unmistakably in the second dorsal, where 

 a slender pointed process projects forward on either side from the base of the transverse 



process, a little external 

 to the zygapophysis. In 

 the first dorsal we must 

 hold that this process 

 does not exist, or that it 

 is represented by a small 

 protuberance on the up- 

 per edge of the trans- 

 verse process which is 

 the last of a series al- 

 ready mentioned in the 

 cervical vertebrae, be- 

 ginning very promi- 

 nently on the axis. I 

 shall not attempt to de- 

 cide whether these are 

 to be considered metapophyses, but simply suggest the question. In the 3d dorsal 

 the metapophyses are thicker and continuous with the outer side of the articular sur- 

 faces. Those of the two sides now rapidly become closer together, and instead of 

 springing from the base of the transverse process, they soon spring from the base of the 

 spinous, and they appear as two vertical, quadrilateral plates parallel to one another. 

 With the 6th lumbar, the vertical anterior edge begins to be cut away below, and this in- 

 creasing, they appear nearly triangular. Among the last few lumbars, these plates cease 

 to be parallel, each bending a little outward ; this change increases rapidly and in the 6th 

 caudal they are expanded and nearly horizontal. After this they rapidly decrease in size, 

 appearing only as knobs projecting upward and outward, and with the 15th they disappear. 



Fis;. 9. — 6th Lumbar Vertebra. 



