FA TWA OF THE GOSAU FORMATION. 



665 



and, as usual, consists of a subcircular head (fig. 5), which is directed 

 inward and forward, and a narrower external area. The posterior 

 border of the articulation is nearly straight ; but the anterior out- 

 line is deeply excavated between the head of the bone and the 

 external trochanter. The globose head measures 1 T 7 - inch from front 

 to back ; and may be considered to be inch from within outward ; 

 but the entire length of the proximal articular surface was about 

 3j-^j- inch. The articular surface beyond the head contracts to less 

 than 1 inch from front to back, but widens again to fully 1^ inch 

 at the border of the external trochanter ; as in Cryptosaurus eume- 

 rus, the narrower external part of the articulation is concave from 

 within outward, and does not extend so far proximally ■ as the 

 convex head by half an inch. The length of the bone to the distal 

 border of the head on its inner margin is not more than 9 inches. 



The anterior proximal trochanter (fig. 5) is about 1| inch long, and 

 convex in length ; so that it dies away both distally and proximally, 

 where it merges in the articular surface. It is rough with oblique 

 muscular markings, and rounds into the flattened but slightly con- 

 vex external surface, which is also roughened, with a triangular area 

 of muscle-marking 2j? inches long, which tapers distally. Below 

 this area the external side loses its flattened aspect, and becomes 

 rounded from front to back. 



The proximal half of the shaft is considerably compressed from 

 above downward, and is flattened on both aspects : its width from 

 within outward in a line with the distal limit of the proximal tro- 

 chanter is about inches, an d just above the lateral inner trochanter 

 about ly 7 ^ inch, while just below the lateral trochanter the width 

 is about l^j- inch ; and there, as the shaft becomes narrower, it 

 grows more convex from side to side. The superior or anterior 

 aspect of the bone is marked with a strong longitudinal muscular 

 ridge, which originates towards the hinder part of the articular ball, 

 curves a little outward and then inward, and extends as nearly as 

 possible in the middle line of the shaft for a length of 6± inches ; 

 it is moderately elevated, strongest proximally. and dies away where 

 a distal flattening of the bone gives an aspect of flexure to the lower 

 part of the shaft. There is also a second muscular ridge, which 

 originates at the same point, below the outer limit of the proximal 

 head, and, running obliquely inward, curves round the convex inner 

 side of the bone and becomes merged in the proximal limit of the 

 trochanter. Both these ridges are less marked than in the larger 

 species. 



The posterior aspect of the shaft(fig. 4)is much more flattened. The 

 strong muscular ridge to which I have already referred as defining 

 an area homologous with the obturator-region of mammals, extends 

 distally for nearly 3 inches, and then curves more sharply inward 

 to merge in the inner trochanter. Prom this ridge extend obliquely 

 inward, so as to cross each other, two series of narrow straight 

 linear muscular markings. Parallel to the sigmoid curve of the 

 proximal articular margin, and about a quarter of an inch below it, 

 is a line of about six or eight circular vascular perforations. 



