66 NEW YORK STATE MUSEUM 



one of the consolidated bone in question, and behind with the first 

 one of the pelvis. 



The 15th vertebra in Circus has a pair of true ribs, i. e. they 

 are connected with the sternum through the intervention of costal 

 ribs or haemapophyses, the two being freely articulated. This pair 

 of pleurapophyses also has unciform appendages, that on either 

 side anchylose on the lower third of the rib, their apexes being di- 

 rected upward. 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 pleurapophyses. The 

 facets for the tubercles are at the ends of the diapophyses and look 

 directly downward and outward throughout this region. 



The vertebral ribs of the 16th to .the 19th vertebra inclusive be- 

 come gradually longer as we proceed backward ; they all bear 

 large anchylosed unciform appendages, with their apices directed 

 backward, of a form shown in figure 25. They are laterally com- 

 pressed and offer large articulatory facets for the costal ribs. 



The sternal rib of the 15th vertebra, the first of the series, articu- 

 lates high up on the costal process of the sternum. It is short and 

 straight. As we proceed toward the pelvis we find them becom- 

 ing gradually longer, flatter from side to side, and more curved 

 upward, their convexities being below. They articulate with the 

 sternum by extensive transverse facets [fig. 25]. 



The two leading vertebrae of the pelvis each have a pair of ribs 

 also, that in no way differ from those that I have just described, 

 excepting that the last pair is without fully developed 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 transverse 

 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 sternum [fig. 25, 26]. In outline, 

 the general form of this bone in Circus, viewed from 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. Similar openings 

 occur also on the interfacial spaces on the costal borders ; in groups 



