AXIAL SKELETON OE THE STEUTHIONID^. 9 



foramina are placed between this vertebra and its successor. The diapophysis has 

 aborted or has become fused with the neural spine. 



The twenty-eighth vertebra (fig. 9, 5) seems to answer to the thirty-second vertebra of 

 Stntthio, but is not concave either ventrally or laterally. I am unable to say whether 

 its neural arch is deplaced or not. There is no diapophysis ; and the parapophy^s may 

 be absent, or it may (as in No. 1.361 e) be present as a process abutting against the 

 preacetabular process of the ilium, like the parapophysial process of the twenty-seventh 

 vertebra, but considerably smaller than the latter in all its proportions. 



The vertebrae from the txventy-ninth to the thirty-second inclusive^ are devoid of trans- 

 verse processes, but have a pair of superimposed neural foramina at the postaxial ends 

 of their neural arches. A median hypapophysial keel extends postaxially, beginning 

 beneath the thirtieth vertebra. The last (thirty-second) vertebra may send a thin para- 

 pophysial lamella to abut against the ilium, and so resemble the vertebrae of the next 

 category. These vertebrae without transverse processes might be distinguished as 

 Lumbo-Sacral Vertebra, a category not present in Struthio, in which genus these 

 vertebrae have parapophyses, as have also the more postaxial lumbar vertebrae. 



THE SACRAL VERTEBRA. 



The thirty-third vertebra. — This is the first vertebra which normally develops a 

 transverse process (fig. 8, t), abutting against the postacetabular (or rather, here, supra- 

 acetabular) part of the ilium. This transverse process seems, in the young, rather 

 diapophysial than parapophysial in its nature ; but with age the plate descends to a 

 lower level. There is a strong median subvertebral keel. 



The thirty-fourth vertebra. In this vertebra the parapophysis becomes more conspi- 

 cuous (fig. 8, 2})- In the young it is seen to form (as in Struthio) in conjunction with 

 the diapophysis (d) a flattened surface for the ilium. The vertebra is generally smaller 

 than is its serial predecessor ; but the median subvertebral keel is well developed. 



The thirty-fifth vertebra is like its predecessor, but smaller generally, while the united 

 di- and parapophysial surface (on each side) is larger. 



With age, as the adult condition is gradually attained, the sacral vertebrae become 

 draw n relatively preaxiad through the much less rapid rate of increase of the last five 

 lumbar vertebrae (twenty-eighth to thirty-second). Thus these vertebrae become rather 

 supraacetabular in position, as in Struthio, than postacetabular ; and thus the vertebral 

 column hardly appears, as it does in Struthio, at the bottom of the acetabulum when 

 the pelvis is viewed laterally. 



THE SACRO-CAUDAL VERTEBRA. 



The thirty-sixth vertebra. — In the young this vertebra has a tolerably developed 

 centrum and a transverse process (formed of both di- and parapophysis) abutting 

 ' It may be the 28th to the 32nd, or only the 29th to the 3lBt, that are thus devoid of transverse processes. 



voii. X. — PART I. No. 2. — March, 1877. c 



