114 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [YoLYl. 



some size, to whicli these terms are applied. Externally and poste- 

 riorly the margin is roughened for the attachment of ligaments that bind 

 the head of the diminutive fibula to this bone. In the middle of this 

 articular surface is to be seen a tuberosity, on either side of which are 

 the depressions for the femoral condyles. Produced downwards, ante- 

 riorly from the rotular ridge are the cnemial ridges ; these have their 

 crests bent slightly outwards, and they merge into the shaft below, 

 abreast the superior point of the fibular ridge. Of the two, the outer 

 or ecto-cnemial is the shorter ; that is, it does not extend so far down 

 the shaft as the inner or pro-cnemial. They have between them an 

 ovate concavity, with the larger end above, the lower end subsiding 

 upon the shaft with the ridges themselves. The vertical elevation on 

 the external aspect of the shaft for articulation with the fibula runs 

 down the side but a short distance ; a little below its abrupt termination 

 may be observed, in a line with it, the nutrient foramen, entering very 

 obliquely from above downwards. After leaving the fibular ridge as far 

 as the point where the bone begins to expand transversely at the distal 

 extremity, the shaft is remarkably smooth and nearlj^ cylindrical. This 

 transverse and distal expansion is checked, both anteriorly and pos- 

 teriorly, by abruptly meeting the distal condyles, the point of meeting 

 perhaps being rather the higher behind. The condyles, differing 

 but little in size, are singularly uniform as to shape, with their curved 

 surfaces downwards, being flat on their outer aspects, with a raised 

 rim bounding them in each case. They stand out prominent and apart. 

 Anteriorly their convex surfaces are the widest, behind they slightly 

 approach each other, and the articular convex surface is narrowest on 

 the outer condyle. The intercondyloid notch is deep, and appears 

 equally well marked throughout its extent. Immediately above it, ante- 

 riorly, there is a deep triangular depression ; another, and more shallow 

 one, is found behind in the corresponding locality. Up the shaft a short 

 distance on the inner side, anteriorly, is a little tubercle, to which is at- 

 tached the ligament that binds down some of the strong tendons of the 

 extensors. This ligament crosses the anterior triangular depression 

 mentioned above, obliquely, to be inserted near the external condyle 

 superiorly. This is the arrangement also in Bubo mrginiamis, but in 

 some of the Hawks this ligamentous bridge has become thoroughly ossi- 

 fied, forming a strong bony band across the concavity in question. It 

 is interesting to remark here, however general the rule may be as ap- 

 plying to the diurnal and nocturnal Eaptores, that whereas this band is 

 ligamentous in the tibia in some of the Owls, a bony one fulfilling the 

 same function is found in them just below the head of the tarso-meta- 

 tarsus; these conditions are just reversed among some of the Hawks. 

 Usually, in old birds of this species, the fibula is firmly anchylosed to the 

 entire length of the fibular ridge of the tibia ; arching outwards, its head, 

 surmounted by an antero-posteriorly elongated facet, rises a little above 

 that bone at the point where it is attached to it by ligament. This is 



