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serial line. The second lumbar carries a pair of riclge-like hypo- 

 pophyses, but these are quite rudimentary on the vertebrae both in 

 front and behind; and are not distinguishable on the fourth. 



Reckoning as sacral vertebrae all that are ankylosed, 

 these are six in number. The fusion is complete, but the 

 number of the constituent vertebne is revealed by transverse 

 ridges on their ventral surface at the junctions of the bodies, as 

 also by the foramina of exit of the spinal nerves. 



The sacrum. — PI. IX., figs 1 — 4. The conspicuous feature of 

 the sacrum is an enormous development and fusion of the meta- 

 pophyses of the constituent vertebne, which, thus expanded and 

 fused, form a roof, which overhangs the pelvis (figs. 1, 2 and 4 

 mm). This is widest anteriorly, where also it can be seen to be 

 serially continuous with the metapophyses of the lumbar ver- 

 tebrae; it then narrows slightly, and posteriorly, it widens into 

 two diverging processes (tig. 2). With the under surfaces of 

 the anterior and posterior extremities of this overhanging metapo- 

 physial roof are fused the ilia and ischia respectively. 



The spinous processes (fig. 2 s) are also ankylosed, forming, in 

 front, a keel-like ridge, but behind, the superior edge of this ridge 

 expands laterally into a wide lamina, which, extending outwards, 

 meets, or nearly meets, the fused metapophyses and thus forms 

 either a completely closed canal, or, in the parts where the 

 two elements have not completely met, a deep groove. Into 

 this canal or groove, as the case may be, open large foramina 

 for the posterior divisions of the spinal nerves. The transverse 

 process of the first of the sacral vertebra is like that of the last 

 lumbar, but stouter and points rather more downwards. The 

 remainder of these elements are fused into an arched lamina 

 (fig. 1 tr) which is ankylosed with the ilium in front and 

 the ischium behind. This lamina is perforated by large foramina 

 for the inferior divisions of the spinal nerves. 



The first sacral vertebra bears anterior zygapophyses with 

 concave facets for articulation with the posterior zygapophyses of 

 the last lumbar, and similarly, there are small zygapophysial pro- 

 cesses with facets for the first of the caudal series (fig. 3 p^.). 



The Tail. — The caudal vertebrae are twelve in number, the 

 tenth and eleventh being nothing more than rounded nodules, 

 and the last a plano-convex plate (PI. V., figs. 1 and 2). 



The bodies, of the first four or five, are rather elongated ; the 

 spinous process broad and distinct on the first two or three, 

 subsequently diminishes in size to the fifth or sixth of the 

 series, where it disappears as a distinct median process, and is 

 afterwards represented by a minute tubercle on each side of 

 the mid-line. 



The transverse processes are flat and rather broad in the first 



