■No.5.] SHUFELDT ON THE OSTEOLOGY OF EREMOPHILA. 145 



"rotular channel," soon to disappear into internal and external condyles. 

 The larger and lower external condyle is longitudinally cleft posteriorly, 

 so as to afford an additional and outer condyloid surface for the head of 

 the fibula, with which it articulates. 



A tuberosity is found behind, just above this cleft, and a few others, 

 less prominent and situated more internally, are seen on this aspect of 

 the bone, in the popliteal fossa. 



The limiting margin of the internal condyle is sharp and distinct. 

 The ordinary features, as tuberosities and muscular lines and markings, 

 usually sought for at this end of the bone in nearly all birds, are very 

 feebly reproduced in our present subject. 



The proximal extremity of the tibia has a very interesting form, due 

 to the prominence of the cnemial ridges. These are attached to the head 

 of the bone, well above the horizontal articular surface for the condyles of 

 the femur. Their superior border is continuous and convex upwards ; 

 their inferior borders meet the shaft abruptly, and there terminate. 

 Both of these wing-like processes are turned towards the fibular side of 

 the bone, the procnemial process being the larger in every respect ; and 

 the ectocnemial sometimes is ijroduced downwards into a very sharp 

 and needle-like spine, a characteristic of other Oscities. They include 

 between them a triangular concave and rather deep recess. The expan- 

 sion supporting the superior articular surface projects over the shaft af 

 the bone in all directions, being quadrilateral in outline, and having an 

 articular facet for the fibula on the outer side, while in the middle 

 of the surface, above, a tuberous spine of the tibia exists, with concavi- 

 ties on either side for the condyles of the thigh-bone. ' 



The shaft is remarkably straight, light, and hollow, though apparently 

 non-pneumatic, no apertures having been discovered to allow the air 

 access to the interior. 



A fibular ridge, 4 milUmetres long and 1 millimetre deep, is developed 

 in the upper third of the shaft, perpendicular to its outer aspect, for the 

 lower articulation of that bone. 



Huxley and Gengenbauer maintain that the distal extremity of the 

 tibia represents the astragalus among the Class Aves, and there certainly 

 seems to be some foundation for this assertion, for if we examine this 

 bone in the young of any of the Gallince, as in Centrocercus, -we find the 

 segment that eventually ossifies with this end of the tibia to be rather 

 too extensive for a mere epiphysis, and may represent that tarsal bone. 

 Without further remark, then, upon this important and still unsettled 

 question here, -we will observe that in UremopMla, and in all birds, the 

 leg-bone terminates distally by two anteriorly placed condyles, separated 

 by a well-defined intercondyloid notch. These condyles, approaching 

 each other behind, diverging in front, are reniform in outliue and shape, 

 with their convex surfaces downwards. They are higher on the shaft an- 

 teriorly, and the articular portion is more extensive. Likewise, anteriorly 

 the shaft is grooved below, to be bridged over just above the " notch" by 

 10 G B 



