18 Osteology of Circus hudsonius. 
above, is a parallelogram. Its superior or dorsal surface is deeply 
concave, accompanied, of course, by a corresponding convexity 
of the pectoral aspect. ‘The middle of the median line above 
presents a row of pneumatic foramina leading to the keel. Simi- 
lar openings occur also on the interfacial spaces on the costal 
borders ; in groups just within the costal borders and the anterior 
border of the body; and at the bases of triangular pits, one of 
each, which occupy the inner aspects of the costal processes. 
The hinder border of the sternal body is gently concave, and 
in the specimen in hand the right side is pierced by two foramina, 
Peg, &. Fxg. A 
Fig.8. The sternum of C7rcus, viewed from below, I have specimens 
before me wherein the sternal foramina are exceedingly small, and 
I should not be at all surprised to find a sternum of this Hawk 
lacking these foramina entirely. i 
Fig.9. Heeds of scapula, clavicle and coracoid, inner aspect, showing 
their mutual relations. s. scapula; c/. clavicle; and c. coracoid. 
Same specimen as Fig. 7. Life size from nature, 
while only one occurs on the left, as shown in Fig. 8. "The 
sternum of /alco sparverius has a large elliptical foramen on 
either side, whose peripheries so far encroach upon the posterior 
margin of the sternal body as to slightly absorb it at the point of 
tangency. In Falco richardsonii these foramina are well within 
this border. 
But one pair of muscular lines presents itself upon the other- 
wise smooth ventral surface of the sternum of Circus. Two of 
the lines are seen on each side of the keel (Fig. 7). The carinal 
