GIG-ANTIC BIED EEOM LOWER EOCENE BEDS. 147 



curvature. The position and extent of the fibular articulation [fib. art) is shown in the 

 figures 1 & 2 between the two stars (*). In this region, especially towards the upper 

 part, the hinder surface of the bone is flattened, and a shallow groove runs along close 

 to the fibular articulation, ending in the aperture for the tibial artery (PI. XXVIII. 

 fig. 1, t.a) near its lower end. The front and inner sides of the bone, at the upper part, 

 are rounded, while the outer side is angular. The inner and outer sides retain these 

 characters, more or less, throughout their length ; but the anterior and posterior 

 surfaces reverse their characters, that is to say, the front surface which is convex above 

 becomes less so in the middle of the shaft, and towards the lower end it is flattened 

 and then deeply grooved. The hinder surface soon loses the flattening of its upper 

 part and at its lower end becomes regularly rounded. About 3 or 4 inches of the 

 proximal part of this tibia are undoubtedly wanting, but the commencement of the 

 buttresses, which spread upwards to form the cnemial crests, are still to be seen. The 

 beginning of the outer crest is shown in fig. 2, at the upper end and a little in 

 front of the fibular articulation, but is only traceable for a very short distance down 

 the front of the bone. Nearly in the middle of the upper end of the shaft is the 

 beginning of the anterior cnemial crest, and from this a ridge runs downwards and 

 inwards so as nearly to reach the inner side of the shaft about halfway down. Con- 

 tinuing downwards this ridge becomes rougher and forms the inner edge of the tendinal 

 groove (t.c). On the inner side of the upper end of the shaft a portion of the internal 

 articular rugosity is preserved (i.a.r). 



Measurements of tibio-tarsi in millimetres. 



Specimen Specimen 

 No. 1, fig. 7. No. 2, fig. 2. 



Greatest width from inner to outer tuberosity 105 90-3 



Greatest width across front of condyles ....... 92 84 ■ 5 



Greatest width across back of trochlear surface 69 



Greatest antero-posterior extent of inner condyle .... 105 



Greatest antero-posterior extent of outer condyle .... 79 



Width of lower aperture of bridge ......... 14 12-0 



Narrowest part of bridge between upper and lower apertures . 20 19 - 

 Antero-posterior diameter of shaft one inch above bridge . . 33 



Lateral diameter of shaft one inch above bridge 61 



Antero-posterior diameter at middle of fibular articulation . ... 36*0 



Lateral diameter at middle of fibular articulation 50'0 



Probable length of bone when complete 590 510-0 



The third portion of a tibio-tarsus (PL XXIX. fig. 12) consists of about six inches 

 of a left shaft immediately above the bony bridge. The depth and position of the 

 groove, as well as the general form of the bone, agree with the specimens above 

 described, and I have no doubt as to their belonging to the same kind of bird. On the 



