OSTEOLOGY OF CARNIVOROUS DINOSAURS. 



67 



In discussing the use of the large foot on the pubis Marsh' says: The only probable use is that it 

 served to support the body in sitting down. That some Triassic dinosaurs sat down on their ischia is 

 proved conclusively by the impressions found in the Connecticut Ri\er sandstone. In such cases the 



leg was bent so as to bring the heel to the groimd. 

 the foot of the pubes to the ground, nearly or quite 

 under the center of gra\ity of the animal. The 

 legs and ischia would then naturallj' aid in keep- 

 ing the body balanced. Possibly this position 

 was assumed habitually by these ferocious biped 

 reptiles while lying in wait for prey. 



When in position (pi. 13) the pubes 

 project forward and downward. Seen 

 from the front they form a Y-shaped 

 figure (pi. 11, fig.l). Their distal ex- 

 tremities are usually found firmly coos- 

 sified though occasionally immature in- 

 dividuals have them separate. Above 

 this point of contact they were separat- 

 ed by an elongate aperture 120 mm. in 

 length in 4734, U.S.N.M., while above 

 this aperture they meet again forming 

 a strong pubic symphysis. Wliere the 

 anterior ends of the distal portion pro- 

 ject forward there is a deep notch be- 

 tween the pubes of opposite sides on the 

 median line as shown in figure 1, 

 plate 11. 



The same action in the present group would bring 



MeoMLrements of pubes of Antrodemus valens Leidy. 



Ischium (is.). — In the United States fig. 47.— eight pums of antrodemus valens leidv. 



Nu 



National Museum collections there are 

 three pairs of ischia that pertain to the 

 species Antrodemus valens, all in a good 

 state of preservation. Except for dif- 

 ferences in size, all of these bones closely resemble one another in then- more 

 important features. 



8367, U.S.N.M. J NAT. SIZE. .4, SIDE view, i?, distal view 



OF COALESCED PUBES. 0, ACETABULAR BORDER; is. ISCHIAC 



articulation; p.p. articulation for pubic peduncle of 



THE ILIUM; S, suture BETWEEN DISTAL ENDS OF COALESCED 

 PUBES. 



' Dinosaurs of North America. 1S96, p. 161. 



