Holland : Osteology of the Mosasaurid^e. 



165 



what defective, irregular in outline, the surfaces suggesting that it may 

 have been imbedded in fibrous or cartilaginous tissues. The bifid 

 extremity is broader than the part of the shaft immediately behind it. 

 Viewed from the side the bone is seen to be gently curved, the curvature 

 increasing at the bifid end. It is trough-shaped on the surface which 

 shows longitudinal concavity, and on the surface which shows longi- 

 tudinal convexity has through the middle a raised ridge of greater 

 convexity than the sides adjacent. A deep 

 groove runs from the middle of the convex sur- 

 face, increasing in width and depth until it 

 terminates in the notch at the bifurcating end ; 

 and a similar groove, but much shallower and 

 not so long, though broader, reveals itself on 

 the opposite or concave side of the bone. 

 Numerous short ridges, with relatively deep 

 striae, or shallow grooves between them, appear 

 at the end of the bone in the neighborhood 

 of the deep bifurcation. These do not run 

 back far on the surface, though the entire half 

 of the bone on both flat surfaces toward the 

 bifurcated end shows faint traces of longi- 

 tudinal lines of elevation and depression. The raised central lon- 

 gitudinal ridge, which appears prominently upon the convex side 

 of the bone is joined a little more than two thirds of the length of the 

 bone from its notched end by ridges, which represent thickenings of 

 the bony mass on either side. This is shown in Figure 2. That 

 portion of the bone which lies at the extremity opposite the bifurcated 

 end is in the specimen before us somewhat broken and parts of it ap- 

 pear to be missing. No facets or surfaces distinctly indicating artic- 

 ulation with other bones can be made out with certainty, though they 

 are suggested. The breaks in the bone at this point show that the 

 two flat surfaces are composed of thin laminae of dense osseous tissue, 

 between which there is looser cancellous tissue. 



Fig. 4. Sections across 

 the bone. 1. Section 

 taken at the narrowest 

 part of the shaft back of 

 the bifurcated extremity. 

 2. Section taken at a 

 point about two-thirds the 

 length of the bone from 

 the bifurcating end. 



Dimensions. 



mm. 



Extreme length 290 



Extreme breadth at notched end 50 



Least breadth of shaft back of notched end 26 



Thickness of bone along edges 2-4 



