76 ANATOIVIY OF VERTEBRATES. 



drical form below the great trochanterian ridge, the shaft at its 

 lower half expands transversely, and, in forming the distal con- 

 dyles, also from before backwards, with a bend in that direction. 

 The inner condyle begins anteriorly as a ridge, expanding into 

 a convexity which attains its greatest breadth posteriorly, where 

 it becomes more flattened. The outer condyle, commencing in 

 the same manner, is indented at its broad lower end by an angular 

 groove, which, widening, divides the back part of the condyle into 

 two convexities. The inner of these is the broadest and most pro- 

 duced, is applied to the outer facet of the tibia, and represents 

 the ordinary outer condyle : the more external convex ridge and 

 the groove dividing it from the outer condyle are adapted to the 

 head of the fibula. This is the most characteristic part of the 

 bird's femur. The space between the anterior beginnings of the 

 condyles is the * rotular ' channel : it is usually broad and mode- 

 rately concave transversely, convex lengthwise ; sometimes divided 

 from, commonly continued into, the intercondyloid fossa which is 

 marked with pits for ligamentous attachment. The inner side of 

 the inner condyle is flattened, with a tuberosity at its mid-part, 

 and sometimes a second just above the hind part of the condyle. 

 There is usually a tuberosity above the hind end of the fibular 

 ridge, exterior to which the surface is sometimes flattened, some- 

 times prominent, in Dinornis impressed by a deep fossa. ^ At the 

 lower part of the outer condyle before the ^ fibular ' groove begins, 

 there is usually a small pit. The popliteal depression is divided 

 by a ridge from the intercondyloid one. The shaft shows inter- 

 muscular linear ridges : in Aquila one extends from the fore and 

 outer angle of the epitrochanterian articular surface to near the 

 beginning of the inner condyle ; a second extends from the inner 

 and back part of the upper third of the shaft to the tubercle above 

 the back part of the inner condyle : the third shorter * linea aspera ' 

 is at the back part of the middle third of the shaft near its outer 

 side. In Dinornis a ridge continued from the anterior trochan- 

 terian one bifurcates at the middle of the fore part of the shaft 

 diverging to the beginnings of the two condyles. In Aj)teryx the 

 two posterior lineai aspera? approximate at the middle of the shaft 

 and then diverge to the condyles : in Dinornis they expand into 

 tuberosities, or the inner one alone is continued as a ridge, but 

 interrupted above the condyle : the inner ridge is strongly marked 

 and continued to the condyle in Aptornis. The orifice of the 

 medullary artery is at the back part of the shaft above its middle. 



' In Dinornis maximus the femur is 16 inches in length, and 6| inches across the 

 distal end. 



