338 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [Vol. YI. 



aspect between the greater and lesser tuberosities, a deep fossa that has 

 a great resemblance to the pneumatic orifice externally, and of about 

 the same dimensions, being only separated from that depression by a 

 thin bony wall ; it seems to be designed simply for muscular insertion, 

 and has no communication with the general cavity of the hollow hu- 

 meral shaft. 



The radius and ulna are also singularly typical in their avian charac- 

 teristics, as might have been looked for after our remarks upon the bone 

 of the brachium ; their principal diflterence lies in their being non-pneu- 

 matic, although they are hollow like all long bones. 



In the right arm of Lagopus leucurus, which we have before us, care- 

 fully dried, in its position of rest, with all the ligaments still attached, 

 in situ, we find the radius to be unusually straight, in fact almost in 

 line between the oblique tubercle of the humerus and the bone it meets 

 in the carpus. Its shaft is nearly cyhndrical, and shows a muscular 

 line, upon an otherwise smooth surface, that travels along its proximal 

 two-thirds beneath. Distally it overlaps the cubit by a transversely 

 dilated extreLoity to articulate with its carpal bone. The head of the 

 ulna is large, and betrays the fact that it belongs to a bird of considera- 

 ble power of flight ; the olecranon process is a blunt, tuberous apophysis, 

 slightly bent anconad; the greater and lesser sigmoidal cavities are dis- 

 tinct and fairly marked, particularly the former. 



The shaft of the bone is more than twice the bulk of that of its com- 

 panion, decidedly convex outwards, the curve being greatest at the 

 junction of the proximal and middle thirds; it is elliptical on section, 

 the major axis of the ellipse being vertical. The muscular lines of the 

 ulna are but faintly developed, as are the row of minute tubercles for 

 the bases of the quills of the secondaries. 



Anteriorly the bone displays its usual trochlea head for its own carpal 

 segment ; this surface is bounded palmad by a sharp and even curve, 

 ■convex distally, while the inner articulating surface beneath the ex- 

 panded end of the radius is uneven and applied to the concavities and 

 convexities of the free pair of carpal elements. 



These bones among the Partridges and other Grouse, except in size, 

 present to us no extraordinary departures from the description just 

 given of Lagopus. 



We do not believe there is a bird in our country that can offer us better 

 facilities for the study of the bones of the carpus than the young of 

 Centrocercus uropliasianus. Anchylosis of the various segments involved 

 is exceedingly tardy, and it is not at all necessary for the student of 

 this joint, that has puzzled so many comparative anatomists and orni- 

 thotomists, to seek the primoidal ossicles in the very young chick, unless 

 he desires to ascertain the points as regards priority of ossification of 

 the carpal bones, a question we will evade here entirely, for these bones 

 are quite distinct and easily detached in the bird at six weeks or more 

 ■of age, such as we oifer our reader in the plates. 



