PEOFESSOE OWEN ON THE DICTNODONT EEPTILIA. 
465 
4th. That the junction of the ossa innominata with the vertebral column is effected 
in two ways — by an overlapping or squamous syndesmosis, and by the usual abutments : 
thus the anterior bony wall or surface of the pelvis, analogous to that formed by the 
expansion of the iliac bones in mammals, is here formed by the expanded ribs of the 
first sacral vertebra. 
5th. That the ischium of the right side joins that of the left, and the right pubis joins 
the left pubis; and that both pairs of pelvic heemapophyses are coextended and con- 
fluent, not only along a continuous ischio-pubic symphysis, as in mammals, but so as to 
obliterate the intervening vacuities called ^foramina ovalia seu oltumtoria^' thereby re- 
peating the character of the connate abdominal heemapophyses in the chelonian plastron. 
In the comparison of this new and, at present, unique type of pelvic structure, it is 
interesting to observe, in connexion uith the mammalian tusks in the skull, a mam- 
malian condition of the ischio-pubic symphysis. I lay less stress on the degree of coale- 
scence expressed by the term ‘ innominate bone,’ because in some lizards I have observed 
a like confluence of iliac, ischial, and pubic bones, yet never with that amount of 
expansion of the iliac element which the Bicynodon shows,'’and in which, again, may be 
discerned a mammalian characteristic. If the remains of the huge reptiles of the extinct 
Dinosaurian order had not revealed to us an extent of sacrum so much surpassing that 
of all living Saurians, one would have laid more stress on the character of the six sacral 
vertebrae in the Bicynodon, as repeating that in some mammalia. But in this modifica- 
tion we may not be justified in inferring more than that, like the Megalosaurus and 
Bjuanodon, a heavy trunk was in part supported on a pair of huge hind limbs, and the 
weight thereupon transferred by a larger proportion of the vertebral column in the Bicy- 
nodon than in the prone, crawling Crocodiles and Lizards of the present day. 
As the lacertian characters prevail in the skull of the Bicynodon, so likewise do they 
in the pelvis : the backward production of the iliac bones, their confluence with the 
ischium and pubis, never met with in Crocodiles or Chelonians, and, above all, the 
oblique perforation of the pubis near its acetabular expansion, are all repetitions of 
structures known only, among existing Eeptilia, in the lizard tribes. But the massive 
and entire anterior or ventral bony walls of the pelvis, the thick tumid acetabular halves 
of the pubic bones, and the great expanse of the over- or rather under-lapping pleurapo- 
physes of the first sacral vertebra, are dicynodontal specialities, and suggest immense 
strength in this part of the massive framework of these strange extinct Reptilia. 
Explanation of the Plates. 
PLATE XXIII. 
Bicynodon tigricejjs. 
Fig. I. Front view of pelvis: nat. size. 
Fig. 2. Side view of pelvis: ^ nat. size. 
