FROM THE CAMBRIDGE GREENSAIH). 



217 



upward. The superior aspect of the shaft, which the articulation 

 terminates, is concave ; and the concavity runs into the middle of 

 the articulation to give it its crescentic or comma-shaped form (fig. 9). 

 In the Nilotic Monitor this depression receives a talon-like spur from 

 the proximal epiphysis. The anterior margin of the bone below 

 the articular head is concave as it extends distally, but the pos- 

 terior margin of the superior aspect of the shaft was thicker, tro- 

 chanteroid, and probably convex in length ; though, being a little 

 abraded, it can only be seen to widen and inflate the bone below 

 and behind the articulation. As already remarked, the shaft is tri- 

 angular ; and I am disposed to term the other two sides of the bone 

 anterior and posterior, as they lie in front of or behind the inferior or 

 great trochanter. At its fracture the shaft measures one ceritim. 

 from above downwards, and 9 millim. from side to side ; the outline 

 is flat above and behind, more convex and wider at the inferior tro- 

 chanteric margin than at the other angles. 



The great trochanteric ridge extends longitudinally on the middle 

 of the underside (fig. 10), converging rapidly downward to the shaft, 

 and is vertical to the superior aspect of the shaft, like the stem of a 

 capital T : the thickness through the bone at its proximal termi- 

 nation is about 17 millim., though the superior proximal expansion 

 of the articular surface increases the thickness of the bone to about 

 22 millim. This characteristic lacertilian trochanteric process ex- 

 tends to within nearly a centimetre of the proximal extremity of 

 the bone ; it is concave in length, curving forward proximally, is 

 about 6 millim. thick, and somewhat flattened below, with the 

 anterior margin rounded. 



The anterior aspect of the bone is concave, so that the constriction 

 of this side, combined with the concavity of the superior surface, gives 

 a well-defined character to the articular head, almost like a neck, if 

 it were not that these sides jMfnvefge~anteriorly to form a sharp ridge 

 which unites them, and" oecomes flattened as it extends down the 

 shaft. There is a mark of strong muscular attachment, of which a 

 centimetre is preserved, which commences one centimetre below the 

 trochanteroid ridge, on the inferior border of its anterior aspect. 



The posterior aspect of the bone can only be described as saddle- 

 shaped, being convex in length and channelled with a wide, smooth, 

 concave depression, which lies between the inferior and superior 

 trochanters, and curves forward beneath the articular head. The 

 width across the trochanters, where greatest, is 18 millim. There 

 is a small pit about 3 millim. in diameter, which lies immediately 

 behind and below the posterior trochanteroid margin, so as to be 

 between that process and the narrow termination of the articulation 

 of the proximal articular surface. Owing to the posterior thickening 

 of the lateral margin of the great trochanter, its inferior border is 

 wider than the part which rises from the head. 



There is no existing lacertilian which this fossil closely resembles. 

 Compared with the Monitor, the more striking differences are that 

 the fossil has the articular surface more developed on the upper and 

 anterior parts of the head, so as to form a deep concavity in the 



Q.J.G.S. No. 170. q 



