1871.] 79 [Dwight. 



left ilium and the left ischium on one side, and the extremity of the 

 sacrum and caudal vertebra? on the other, two plates of bone are 

 inserted, uniting with one another at a right angle by a transverse 

 line of union (1, 2, 3, 4). The upper, nearly horizontal (1, 2, 3), 

 plate and the deflected vertebrae close the space between the two 

 iliac bones almost completely, while the lower vertical plate (2, 3, 4) 

 shuts off about two-thirds of the opening behind. 



The transverse line of union of the two plates (1-3) is an inch and 

 a half long, with a well marked process at each end. The outer sur- 

 face of the horizontal plate presents little to be described. The ver- 

 tical plate has a ridge (5-4) dividing it into a right and a left por- 

 tion, each of which is roughly triangular. There is an oval foramen 



(6) at the outer superior angle of the left portion, and a smaller one 



(7) at the left upper angle of the right portion. Viewed from 

 within we find the upper part of the interposed bone to be divided 

 by a framework into two fossae, of which that to the right is much 

 the larger, and into each of which one of the lately described fora- 

 mina opens. A careful comparison with the normal pelvic bones will 

 show very strikingly that the upper plate of the abnormal bone cor- 

 responds to the renal portion of the ilium, and the lower to the 

 ischium. And what is more interesting is that the ridge on the outer 

 side of the latter and the framework on the inner side of the , 

 former, together with the general lateral symmetry of the two halves, 

 make it probable that they represent the fused supernumerary bones 

 of the two sides. The viscera had been removed before the impor- 

 tance of these homologies was evident, but the well marked addi- 

 tional renal cavities make it very probable that there was at least 

 one additional kidney. 



A muscular bundle, having a circular attachment about half an inch 

 in diameter, arose from the outer aspect of the vertical plate, and at 

 a distance of an inch and five-eighths from its origin, was inserted into 

 the summit of the third leg. (Fig. 3). The chief bone (a) is two 

 and a half inches long, compressed laterally above so as to be very 

 slender, but expanding below to a breadth of a third of an inch; its 

 lower end is bent forward and has a groove on the anterior surface, 

 the posterior being plane. The lower extremity is bifid. On the 

 anterior aspect, near the lower end, there is a small elevation shaped 

 like a compressed V inverted. The superior end of the bone is sur- 

 mounted by a delicate process which, turning suddenly to the right, 

 ends in a knob. The bone appears to represent the metatarsus of 



