HATCHER: OSTEOLOGY OF HAPLOCANTHOSAURUS 19 
of the neural arch there is a second prominence less pronounced, however, than that 
on the centrum. In the thirteenth caudal the prominence on the centrum is only 
faintly distinguishable. In the succeeding vertebre it has disappeared entirely, 
while that on the neural arch continues on the thirteenth, fourteenth and fifteenth 
caudals, but is wanting on the succeeding vertebree. Of these prominences or tuber- 
osities the superior or that one situated on the neural arch doubtless represents a 
rudimentary diapophysis, while the inferior or that situated on the side of the centrum 
may be considered as homologous with the parapophysis. 1t would, therefore, appear 
as though the transverse processes in the anterior caudals were made up of the coal- 
esced diapophyses and parapophyses. Just what bearing this may have on the exact 
homologies of the so-called sacral ribs in the Sauropoda it is impossible to say. It 
would appear, however, that Osborn’s assertion that a “sacral rib is not a transverse 
process’’° is open to criticism when that term is applied to these elements in the 
dinosaur pelvis, or at least needs some further support, and that Marsh’s statement 
that ‘each sacral vertebra supports its own sacral rib or transverse process’? may 
not have been so far from correct as Osborn supposed it to be, though Marsh’s 
assertion that the sacral vertebree in the Sauropoda were without diapophyses is 
doubtless erroneous. If, as Osborn asserts: ‘“‘ The sacrum of Sauropoda (Cetiosaurs) 
is reinforeed by the addition, not of dorsals, but of anterior caudals,” it would seem 
quite evident that those elements which spring from the sacrals and give support to 
the ilia are in reality only the modified transverse processes of the caudals, and since, 
as has already been shown, the latter appear to have been formed by the union of 
parapophyses and diapophyses, there would seem very good reasons for assuming that 
the so-called sacral ribs which spring directly from the sacral centra are homologous 
with the parapophyses, while the superior bar giving support to the superior border 
of the ilium represents the diapophyses and that these two elements with the con- 
necting diapophysial lamina together constitute the transverse process. According 
to this interpretation the so-called sacral ribs become morphologically quite distinct 
from those elements in the tailed Amphibians as described by Flower on page 66 of 
his “ Osteology of the Mammalia,” and I am inclined to the opinion that, while the 
articulation of the ilium with the sacrum in the Hell Bender (Menopoma) and other 
allied forms is by means of a sacral rib interposed between the ilium and the trans- 
verse process of the sacral vertebra in the Sauropoda as well as in all the other terrestrial 
vertebrates requiring more or less rigidity in this region this interposed sacral rib, if 
it ever existed, has disappeared altogether, allowing the ilium to come in direct con- 
tact with the transverse processes of the sacrum. In Menopoma the transverse proc- 
°>See Memoirs Am. Mus. Nat. Hist., Vol. I., Part V., p. 202. 
