Osteology of Circus hudsontus. 17 
nineteenth vertebra of this little falcon is free and articulates with 
the posterior one of the consolidated bone in question, and behind 
with the first one of the fielvis. 
The fifteenth vertebra in Circus has a pair of true ribs, z. e., 
they are connected with the sternum through the intervention of 
costal ribs or hzemapophyses, the two being freely articulated. 
This pair of pleuropophyses also have unciform appendages, that 
on eitner side anchylose on the lower third of the rib, their apices 
being directed upwards. ‘The facets for the heads of this pair of 
ribs are upon the anterior margins of the neurapophyses, just 
above the centrum of the vertebra. This position of these facets 
obtains for the remainder of the series of articulated pleurapo- 
physes. The facets for the tubercles are at the ends of the diapo- 
physes, and look directly downwards and outwards throughout 
this region. 
The vertebral ribs of the sixteenth to the nineteenth vertebra 
inclusive become gradually longer as we proceed backwards ; 
they all bear large anchylosed unciform appendages, with their 
apices directed backwards, of a form shown in Fig. 7. They are 
laterally compressed and offer large articulatory facets for the 
-costal ribs. 
The sternal rib of the fifteenth vertebra, the first of the series, 
articulates high up on the costal process of the sternum. It is 
short and straight. As we proceed towards the pelvis we find 
them becoming gradually longer, flatter from side to side, and 
more curved upwards, their convexities being below. They artic- 
ulate with the sternum by extensive transverse facets (Fig. 7). 
The two leading vertebra of the pelvis each have a pair of ribs 
also, that in no way differ from those that } have just described, 
excepting that the last pair are without unciform processes. 
They otherwise simply continue the series, and it is evident that 
the arrangement presents seven pairs of pleurapophyses, which 
are connected with the sternum through the articulation with an 
equal number of pairs of haemapophyses, which in their turn 
articulate with the costal borders of the sternum by their trans- 
verse facets. Both the true and costal ribs of this Hawk are 
pneumatic. 
We will now for a moment leave the vertebral column proper 
and pass to the consideration of the s/ernum (Figs. 7 and 8). 
On outline, the general form of this bone in Czvcus, viewed from 
