380 /vNNALS OF THE CaRNEGIE MuSEUM. 



cnemial process in the true Petrels, while in the Shearwaters {Puf- 

 finus) its summit is more generously and characteristically extended, 

 constituting a certain fades that is unmistakable. 



At the distal end of this tibiotarsus of ^strelata vocifcrans we 

 note the deep, longitudinal groove for tendons anteriorly, spanned 

 below by the minute osseous bridge to confine them within it. The 

 condyles are prominent here owing to the deep intercondylar valley 

 between them. Posteriorly they are sharp-edged, and the space be- 

 tween them is much shallower. Externally, we note the thin, fibular 

 ridge for articulation with the fibula, which latter is but a feebly 

 developed bone, lightly attached to its larger companion by a scanty 

 ligamentous attachment. The lower free end of the articulated fibula 

 reaches down to about the junction of middle and lower thirds of 

 tibia's shaft, ^^ and it is here reduced to almost hair-like dimensions. 



Petrels, as a rule, have a slenderer tarsomctatarsus for its length 

 than have the Shearwaters and some other Tubinares (compare figs. 

 106-110, PI. XXVIII; also figs. 20 and 24) ; while at the same time 

 its characters are pretty much the same. In a series of the bones its 

 length runs 3.4 cms., 3.5 cms., and so on, which is about the average 

 for them. At the summit we find the twin articular concavities for 

 the femur well marked, and a well-developed intercondylar eminence 

 between them on the anterior border. The hypotarsus is rather short 

 except upon the inner side, where it is continued down its upper third 

 of the shaft as a thin, lateral plate of bone. For the rest it is com- 

 posed of three processes, 3.7 mm. deep, dividing it into two deep 

 grooves for the passage of the usual tendons of the muscles of the 

 leg. 



The shaft is straight and strongly grooved, both anteriorly' and 

 posteriorly, for its entire length, longitudinally. Passing to the distal 

 trochlccr, it is to be noted that the central one is considerably bigger 

 than either of the others, while it is also placed lower down and more 

 to the front. The inner one is the highest up and situated the farthest 

 to the rear, w^hile the outer one holds an intermediary position. Be- 

 tween these three trochlea, grooves are carried up a short distance 



18 As slender as the attachment of the fibula to the tibiotarsus is, I find 

 one specimen in which the two bones did not part company, notwithstanding 

 the long time which mvist have elapsed since the death of the bird to which 

 they belonged; the circumstances under which the specimen was .collected, 

 and the transportation and handling since. 



