MCEEITHEEIUM. 



115 



In the succeeding thoracic vertebree (text-fig. 45) the head of each rib articulates with 

 one vertebra only, by a deeply concave surface {c.f.) situated on the side of the centrum 

 immediately below and in front of the short blunt transverse process {t.f.), on to the 

 base of which the facet may be continued, at least in 12-13. It is doubtful whether 

 the ribs of this region had any tubercular articulation with the transverse processes. 

 In this region also (12-19) the centrum is considerably wider than high, while the 

 neural spine {n.sp.) becomes gradually wider and shorter, and is only slightly inclined 

 backwards. The metapophyses (m.) form qaite prominent pointed processes. 



The lumbar vertebrae (text-fig. 46) are four in number. Their centra become still 

 wider in proportion to their height and have a nearly straight upper border. The 

 transverse processes {t.p.) are again large, and arise on a level with the top of the 

 centrum; in the two posterior lumbars they seem to have been pointed at their 

 extremities. In the form of the neural spine {n.sp.) and the metapophyses (m.) these 

 vertebrae are much like the posterior thoracic. 



Teit-fig. 46. 



^n.sp,. 



Lumbar vertebra of Mosritherium : A, from front; B, from right side. 

 t.p., transverse process ; other letters as in text-fig. 44. ^ nat. size. 



The sacrum (text-fig. 47) consists of three fused vertebrae, the centra of which are 

 low and broad, the shape of their articular ends being a transversely elongated oval. 

 The metapophyses, forming prominent forwardly directed processes, are well developed 

 on the anterior zygapophyses (a.z.). The neural spines (n.sp.) are low and broad. The 

 pleurapophyses are broad and stout ; they unite at their outer ends, being separated 

 only by nearly circular interosseous foramina (io.f.). On their fused outer ends they 

 bear a long iliac surface (il.s.) which looks obliquely upwards in front and directly 

 outwards posteriorly. The ventral surface of the sacrum is nearly flat, except near the 

 edges of the iliac surfaces, where it is somewhat deflected. The posterior surface of 

 the last of the fused sacrals is deeply concave. The following vertebra should perhaps 



q2 



