236 FIELD COLUMBIAN MUSEUM. 
primary caudal structure although they are modified as ilium-sup- 
porting elements. 
The diapophyses, like the sacral ribs, are remarkable for their 
unusual length and slenderness. The first pair arise from the lateral 
surface of the spine and the stout prezygapophyses. Their distal 
ends unite with the sacral ribs in forming the great lateral plates. 
The second and third pairs arise in common from the fused spines of 
sacrals 11 and 11. Distally they diverge to unite with the iliac crest. 
The fourth pair arise independently; they are directed diago- 
nally backward and attach to the border of the ilium above the 
lesser peduncle. Midway between the base of the diapophyses and 
the attachment with the ilium there is a marked rugosity which 
suggests that the diapophysis may terminate at that point and the 
distal portion be made up of the tubercular portion of the rib. This 
could be determined only from the study of a very young specimen. 
The sacral spines are remarkably short and blunt. In structure 
they are made up of a thickened median plate expanded at the crest 
to form a blunt knob, and flanked in the anterior three by a slight 
pair of lateral spinous plates. The first is free, but stands close to 
the second. In structure it resembles the posterior dorsal, though 
its lateral plates have almost disappeared. The second and third 
spines are so firmly united as to show no trace of the line of fusion. 
Their lateral plates arise from the middle of their respective surfaces. 
The fourth and fifth take on the caudal type of structure, which con- 
sists of a median plate expanded into a simple knob at the crest. The 
fourth stands quite close to the third; the fifth is isolated. All have 
marked rugosities on the anterior and posterior margins for the inter- 
spinous ligaments. 
MEASUREMENTS OF SACRUM. 
M. 
Length: of five:sacral-centra.. 2 pales wd gay es 95 
Breadth across second. pair ofvsacralribs.) soi... 4... 1.05 
Breadth across. fifth pair of-sacraliribee. ).. 3... 2.2. a .98 
Height of first. sacral: vertebra 225.3 siege sa.- Siu 5 +. 0s 2 ake .64* 
Height of third sacral -vertebrawcjn8) 0)... 2a oS ee ee . 60* 
Height of fifth’ sacral: vertebra vic tates - c.f of ns stg a ee 535 
Length of centrum 2 105 eee at es 5. et ele a m8, 
Lenegth-of centrum > IRs als Wee espe ce ae gitar .18 
Length of cemtrtma Lik ifthe fests Bel ta cre os ee tre yeep ire 
Length: of centruim “IVs. Vd fread ee eas ee ge .22 
Length of centriim Wigs eae news ile teal a oer ape et an fa 
* Dimension modified by distortion. 
