NO. 16GG. OSTEOLOGY OF CAMPTOSAURUS—aiLMORE. 257 



shelf is given off. The acetabuhir arch is bounded anteriorly by a 

 rather wide but slender pubic peduncle directed downward and for- 

 ward. The posterior peduncle for the ischium is heavy, broadly 

 swelled, with two roughened surfaces, more especially the posterior, 

 which meet at an obtuse angle. The posterior and more inferior one, 

 which is somewhat cupped, is for the articulation of the ischium. 

 The roughened anterior surface appears to be for the attachment of 

 the heavy pads of cartilage and ligaments which bound the pelvic 

 bones together. Posterior to this process the inferior border is a 

 sharp edge, which, as it extends backward gradually turns from a 

 vertical to a nearly horizontal position, with a rounded, thickened, 

 posterior termination. The upper half of the internal surface is 

 smooth and gently concave from end to end. On the low^er median 

 internal surface are roughened cupped depressions, their greatest 

 extent being vertical, for the articulation of the sacral ribs (see 

 X, Plate 15). These surfaces are separated by narrow, smooth, con- 

 cave, nonarticular tracts. A shallow^, roughened longitudinal groove 



Fig. 30. — Left ilium of Camptosaurus browni. Holotype. Cat. No. 4282, U.S.N.M. ; 

 I NAT. SIZE. External view. Anterior end of preacetabular process restorel 



AFTER THAT OF THE LEFT ILIUM OF NO. 5473 (SEE FiG. 29). FROM A PHOTOGRAPH. 



on the thickened internal edge of the shelf -like projection mentioned 

 above, may be for the reception of the transverse process of the fifth 

 sacral. The greatest vertical width of the ilium is over the ischiac 

 peduncle. 



The ilium is one of the most characteristic bonas of the skeleton, 

 and while the description given above shows all of the essential char- 

 acters of the Camptosaurus ilium, it is found that in other species 

 there are great differences of contour and proportion. 



Measurements of Specimen, Cat. No. Ji282, U.S.N.M. 



mm. 

 Greatest length of left ilium from posterior end to center of preacetabu- 

 lar notch 392 



Greatest width over ischial process 75 



Greatest vv^idth from middle of acetabulum 115 



Greatest expanse of acetabulum 161 



The ischium. — The ischium is larger than the pubis and distally 

 consists of a slender rod-like shaft which curves downward with an 

 Proc. N. M. vol. xxxvi— 09 17 



