OSTEOLOGY OF BIRDS 



321 



into the pelvic brim, upon either side, beneath and in front of the 

 acetabulum, while posteriorly it expands to be lost upon the general 

 surface of the ischium behind. When seen from above, on the 

 dorsal aspect, it is to be observed that the sacrum in the postacetabu- 

 lar area has a broadish, spindle-shaped outline, with the parial rows 

 of the foramina in it very minute. For its posterior fourth, the 

 outer margins of the sacrum are very decidedly separated from the 

 mesial borders of the ilia opposite them. The last " sacral vertebra " 

 exhibits all the characters of the first caudal one, even to a well pro- 

 nounced neural spine and neural canal. The three leading caudal 

 vertebrae, at least, are devoid of haemal spines, and their transverse 

 processes are short. 



I now pass to the consideration of the sternum of B r a n t a 

 canadensis. Taking it first upon its ventral aspect, it is to be 

 noted that its general form is oblong, the body of the bone being 

 about twice as long as it is wide, it having an average width of about 

 7.5 centimeters. Its anterior border is thick and strong; an ample 

 keel is developed ; the principal muscular line, on either side, passes 

 parallel to this between outer end of coracoidal groove and the 

 xiphoidal fenestra. It is very distinct, and runs down to the inner 

 side of the " notches " in some of the smaller geese. Posteriorly, 

 the sternum of Branta is one-notched upon either side of the carina. 

 These vacuities are of great size, and almost amount to fenestrae, 

 as they are barely open behind. The lateral xiphoidal processes 

 which they give rise to are long- and narrow, with slightly ex- 

 panded ends, and with a moderate curvature inward. Either one 

 of them is longer than the broad mid xiphoidal projection, which 

 here has its posteroexternal angles markedly produced lateralwise, 

 and its posterior borders at right angles to the plane of the carina. 

 The, keel does not quite extend to the end of the sternal body on 

 this mid xiphoidal process, but spreads out upon it, merging into 

 the general surface. Taking the bone upon lateral view, a costal 

 process is seen to be long in its anteroposterior diameter, low and 

 of uniform hight, with a strong tendency for its anterosuperior 

 angle to be produced forward. The transversely broad costal 

 border faces upward, outward, and backward, while the inter- 

 articular valleys are nearly flat, being pierced by but few pneu- 

 matic foramina. These last, for the most part, are congregated 

 beneath the articular facets for the costal ribs, often converting 

 them into little bridges of bone, a condition well shown in the 

 sterna of Chen and Anser. 



