328 PEOP. ST. GEOEGE MIVAET ON THE 



lumbosacral vertebrae than is the case in any of the Struthionidae, except Ajpteryx and 

 Dinornis. There are three or four ^ true lumbar vertebras. 



The TWENTY-THiKD VERTEBRA (or first true lumbar) resembles its serial predecessor, 

 except that there are no costal articular surfaces, but the transverse process is smooth 

 on its ventral surface, and the centrum is more flattened ventrally. 



The arch formed by the junction between the postaxially extended and dorsally 

 curved parapophysial transverse process of this vertebrffi, and the similarly curved, but 

 preaxially extended, parapophysial transvei'se process of the twenty-fourth vertebra has 

 here become a presacral foramen. 



The TWENTY-FOURTH VERTEBRA is similar to the last described ; but the centrum is 

 smaller, and the parapophysial transverse process more expanded and flattened ventrally. 

 Its presacral foramen is smaller. 



The TWENTY-FIFTH VERTEBRA is almost quite similar to the twenty-fourth. 



The TWENTY-SIXTH VERTEBRA differs from the last in having its transverse process free 

 postaxially, and not uniting with any parapophysis of the twenty-seventh vertebra. 

 The postaxial margin of the transverse process forms the most ventral portion of the 

 preaxial margin of the great lateral acetabular fossa. The diapophysis ascends 

 obliquely dorsad and slightly externad to the ilium, and is generally quite distinct from 

 the parapophysis. 



The intervertebral foramen is mediauly constricted antero-posteriorly so as to 

 approximate to two superimposed foramina. 



The Ltjmbo-sacral Vertebrae. 



These vertebrae are three in number — namely, the twenty-seventh, twenty-eighth, 

 and twenty-ninth. 



These three intimately united vertebrae have the ventral surfaces of their centra 

 narrowing postaxiad and concave transversely, thus forming a continuous plate, antero- 

 posteriorly grooved (Plate LIX. fig. 3). 



Their diapophyses ascend almost directly dorsad, the two more posterior on each 

 side (viz. those of the twenty-eighth and twenty-ninth vertebrae) being visible through 

 the acetabula when the pelvis is viewed laterally (Plate LIX. fig. 2). 



There are no parapophyses, or only minute rudiments of such. The intervertebral 

 foramen behind each vertebra is more or less median, constricted antero-posteriorly. 



The Sacral Vertebrae. 



There are three sacral vertebrae — the thirtieth, thirty-first, and thirty-second ; and 

 they form a series, the centra of which decrease in size postaxially, and continue on 



' Only in the specimens of P. mitratus, No. 70. 3. 30. 1, in the British Museum, have I found this number 

 reduced to three. 



