130 MEMOIRS OF THE CARNEGIE MUSKUM 



At the distal end of the femur the condyles are not very prominent, and the inter- 

 nal one is small. Nor is the rotular channel or the popliteal fossa deep, b\it on the 

 contrary they are both shallower than in many other birds known to me. We find 

 the shaft in tibio-tarsus to be straight and nearly cylindrical. Proximally, the low 

 cnemial process rises but a little above the summit of the shaft, while anteriorly, 

 below it, the pro- and ectocnemial ridges are but very inconspicuously developed. 

 It is between these latter that the small pneumatic foramen usually is seen. Distally 

 the usual characters of this bone are to be observed ; the osseous span to confine tendons, 

 at the antero-distal end of the shaft is present, and passes in a slightly oblique direc- 

 tion over the channel it bridges ; the condyles, with their usual reniform contour, are 

 well separated from each other, and the intercondyloid notch between them, is 

 marked in front, but very shallow behind. In the fibula we see a very slender and 

 rudimentary bone. Especially is this the case below the 'fibular ridge' on the side 

 of the shaft of the bone it articulates with, for it is then reduced to little more than 

 a flattened osseous hair, closely applied to tibio-tarsus, but apparently never actually 

 anchyloses with it. 



Phaethonidse always possess a patella in front of the knee-joint, and it is of an 

 elongated form, being flat behind and convex in front, where it is distinctly marked 

 in the transverse direction by the groove for the tendon of the ambiens muscle. 



Most remarkable of all the bones of the pelvic limb in Phaethon, however, is its 

 tarso-metatarsm. To describe this I select the left one from one of my skeletons of 

 P. tfthereus. The bone is oblong in outline; much flattened in the antero-posterior 

 direction ; and with its middle trochlear process but slightly lower on the shaft 

 than the internal one, which latter in turn is but a little lower than the outermost 

 one. On the summit, the shallow articular depressions for the condyles of the tibio- 

 tarsus are separated by a rounded eminence in front. At the back of the shaft, in 

 this region, we find the " hypotarsus" to consist simply of three vertical ridges, 

 a short, small middle one, with longer and stouter outer ones. Anteriorly, the shaft 

 of the bone is deeply scooped out from above, downwards for nearly its entire 

 length. On the outer side below, this channel terminates in an antero-posterior 

 perforating foramen, situated at a point a little above the notch dividing the 

 mid- and outer trochlear processes. On the inner side below, there is a small, longi- 

 tudinally-disposed groove that runs into the main excavation on this aspect of the 

 shaft at about its middle. This smaller groove also terminates below in an antero- 

 posterior perforating foramen, situated at a point a little above the notch divid- 

 ing the mid- and inner trochlear processes. Thus we see in P. xthcreus, there are 

 two antero-posterior perforating foramina at the distal extremity of its tarso-meta- 



