HATCHER: OSTEOLOGY OF HAPLOCANTHOSAURUS 21 
gous with the true sacral ribs as seen in Menopoma, which to the writer seems ex- 
tremely improbable, it does not follow that they are ‘profoundly different from the 
dorsal ribs” as has been stated by Osborn;° for an examination of a skeleton of 
Menopoma will show the morphological identity of the sacral ribs with the free ribs 
borne at the extremities of the transverse processes alike of the anterior caudals and 
the entire presacral series, while the latter must be homologous with the dorsal ribs 
6 
Fig. 5. Superior view of sacral, anterior caudal and posterior dorsal or lumbar of Menopoma alleghen- 
iensis, twice natural size. s, sacral; c, anterior caudal; d, posterior dorsal; ¢.p., transverse process ; 
s.r., sacral rib; il, ilium; f.r., free rib. 
Fic. 6. Superior view of sacrum, anterior caudal and posterior lumbar or dorsal of Iguana tuber- 
culata, natural size. d, posterior dorsal; s.1, first sacral; s.2, last sacral; c, anterior caudal; t.p., 
transverse process except that on last dorsal which is a free rib ; J, ilium. 
in the terrestrial vertebrates as will become apparent by a study of the skeleton of 
Iguana where the transition from the short straight ribs of the dorso-lumbar region 
to the elongated and curved ribs of the true dorsals is quite gradual. 
In consideration of the characters just described as obtaining in the transverse 
processes of the caudals of Haplocanthosaurus in connection with those already men- 
tioned as pertaining to the sacrum in the various genera of the Sauropoda, it appears 
to the present writer that the following characters relative to the structure of the Sau- 
ropod sacrum as a whole and the homologies of the different elements with those 
of the other vertebrre seem quite probable though not at present capable of being 
demonstrated with certainty. 
First. — That the Sauropod sacrum is composed of five coossified vertebre: which func- 
tion as sacrals. 
Seconp. — That the three median of these five functional sacrals alone composed the 
sacrum in the primitive Sawropoda and may be regarded as the true sacrals. 
5Vol. I., Part V., Mem. Am. Mus. Nat. Hist., p. 201. 
