16 MEMOIRS OF THE CARNEGIE MUSEUM 
the so-called sacral ribs in the succeeding sacrals, does however spring from the 
superior lateral surface of the centrum.. It may therefore be considered as homol- 
ogous with those elements in the true sacrals. Its position with relation to the 
vertebral centrum may be considered as evidence that this vertebra though function- 
ing as a sacral is in reality a modified dorsal and that, contrary to Osborn’s asser-_ 
tion, the sacrum in the Sauropoda may have expanded by the addition of at least 
one posterior dorsal. 
The diapophyses of all the sacral vertebree send downward thin vertical diapo- 
physial lamine. These unite at their extremity with the sacral ribs or as I prefer 
to call them the parapophyses* of their respective vertebree to form thin partitions 
separating the four large sacral foramina to be seen in the inferior view of thig 
sacrum with ilia attached, shown in Fig. 1, Plate V. Internally these foramina are 
enclosed by the sacral centra and externally by the extended iliac bar formed by the 
expanded and coalesced distal extremities of the parapophyses (sacral ribs). 
The parapophyses (sacral ribs) of the first and fifth sacrals are longer but rather 
more slender than those of the three median or true sacrals. This is especially true 
of the first sacral. In this vertebra this element springs from the superoanterior 
surface of the centrum, continues outward for some distance as a strong bar when it 
expands and divides into two branches enclosing a small foramen bounded externally 
by the ium and shown in Plate V., Fig. 1. The inferior of these two branches abuts 
against the base of the pubic peduncle, the superior unites with the diapophysial 
lamina in giving support to the widely expanded anterior blade of the ilium. 
In the posterior sacral the parapophysis springs from the middle of the centrum 
at its anterior extremity and continues as a single bar, only moderately expanded 
distally, where it gives support to the posterior blade of the ilium. Superiorly it is 
united throughout its entire length with the diapophysial lamina. The diapophy- 
sis branches distally and with the posterior blade of the ilium encloses the foramen 
seen in Plate V., Fig. 3. 
The parapophyses of the three median sacrals are all short and stout. They 
differ from those of the first.and fifth sacrals in having their extremities expanded 
and coalesced so as to form a strong iliac bar not only giving support to the ilia but 
constituting the inner superior borders of the acetabula. These three vertebrae were 
the first to become codssified. Throughout the entire life of the individual they 
gave the chief, and during a certain period of its youth perhaps, almost the only 
support to the ilia. It is for these reasons that I consider these vertebree as the only 
true sacrals of which the sacrum in the earliest Sauropods was alone composed. 
‘The homologies of these elements will be discussed more fully when we come to speak of the caudals. 
