344 BULLETIN UNITED STATES GEOLOGICAL SUEVEY. {Vol. YJ. 



of 450 witli the shaft; the head is well formed, spherical, and in all 

 Grouse seems to bear a double depression for the ligamentum teres. 

 Anteriorly below the trochanterian eminence there is an extensive collec- 

 tion of pneumatic foramina. The "trochanter minor" never develoi)S. 



The shaft is smooth, bent slightly forwards ; displays the usual mus- 

 cular lines and the medullary orifice ; it is nearly cylindrical on section 

 about its middle, and before terminal expansion takes place. Below, 

 the rotular channel is very evident, separating the prominent condyles ; 

 of these the external and lower one iDresents the usual fibular fissure ; 

 behind, the popliteal depression is well sunken, one of the muscular 

 lines running into it, and often a foramen is found at its base. Shght 

 fossae are found laterally at the outer surfaces of the condylar enlarge- 

 ments, and sometimes a notch where shaft meets the internal one ante- 

 riorly. Tiie bone is usually slenderer in Bonasa, Pedicoecetes, and Tetrao 

 canadensis. 



Among the OdontopJiorince the femur has the same general character- 

 istics ; it is, however, non-pneumatic^ the double pit for the ligamentum 

 teres is better marked, and the muscular lines are scarcely perceptible. 



The patella is never absent in the Tetraonida;, and occupies its usual 

 position as a free bonelet protecting the anterior aspect of the knee-joint. 

 It accommodates itself to the conformation of the rotular channel, hav- 

 ing a flattened surface superiorly, a rounded border below, and a double 

 surface behind, the most extensive aspect of which is applied to the side 

 towards the internal condyle. 



The proximal extremity of tibia in the young chick of Gentrocevcus has 

 advanced so little toward assuming any of the definite characteristics 

 of the full-grown bird, that, almost in self-defense, we take up for exam- 

 ination the bone from a skeleton of a bkd of the same species several 

 weeks older ; here we discover the superior general condylar surface 

 still capijed with cartilage, and the borders confining it, as yet, but 

 feebly produced. The most interesting point, by far, is the appearance 

 of an unusually large epiphysis, if it may be so termed, fashioned to 

 and resting upon the future location of the " rotular crest." 



Why this bone should be here added we cannot, as far as our knowl- 

 edge extends, exactly comprehend, for in the old and mature birds of 

 any of the Grouse the epi-cnemial crest is never very prominently pro- 

 duced, nor is it in any of their near kin. As age advances this seg- 

 ment becomes thoroughly confluent with the tibia, and leaves no trace of 

 its early existence. 



The head of the bone in the adult Sage Cock is a very substantial 

 affair, with r»ro-and ecto-conemial ridges, that soon merge into the shaft, 

 well produced; the latter ridge is usually dilated on its anterior as- 

 pect, and the rather extensive concavity between them is directly con- 

 tinuous with the shaft below. 



The tibia never becomes pneumatic either in the Grouse or Quails, 

 and in the former sections of its shaft are universally transversely 



