MCKRITJlEIilUM. 
115 
111 the succeeding- thoracic vcrtehric (text-fig. 45) the head of each rib articulates with 
one vertebra only, by a dee])ly concave surface {c.f.) situated on the side of the ceutruin 
iinmediately 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 s])iue [n.sp.) becomes gradually wider and shorter, and is only slightly inclined 
backwards. The metapophyses {pi.) form quite prominent pointed processes. 
The lumbar vertebrie (text-fig. 4G) 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. 
Lumbar vertebra of Mcerltherium : A, from front; B, from right side, 
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 hat, 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 
