SinKKLiri' : Os'i i:(>i,o(;v oi iiii I Iirodionks. 181 



terior angle of the diapophysis. On either side of the beam thus 

 formed very large pneumatic openings are seen in these ultimate ver- 

 tebriB, and the trabeculcc spanning the cavities within are plainly in 

 view. 



Four pairs of h:v;mapophyses articulate with the borders of the ster- 

 num in all of the Herons that 1 have thus far examined ; the fifth pair 

 not reaching this bone, but articulating with the hinder margins of the 

 last sternal pair. The slender i)air of ribs that claim this last pair of 

 hgemapophyses articulate with the twenty-fourth vertebra and it is 

 the first one that anchyloses to form a part of the pelvis. 



The last two pairs of vertebral ribs are without epipleural appendages, 

 and even when these processes do occur on the ribs they are very weak 

 and freely articulated with the border. Herons have very frail ribs at 

 the best, a fact that strikes one the moment we examine the thoracic 

 skeleton of one of these birds. 



The seventeenth vertebra having a small pair of free ribs in the 

 Yellow-Crowned Might Heron, we find has a still longerand better de- 

 veloped pair on the eighteenth in this species, and yet another free pair 

 on the nineteenth. These latter have epipleural appendages, although 

 they do not meet the sternum by costal ribs below. This gives three 

 pairs of free ribs to Nycticorax ; four pairs, as in other Herons, that meet 

 true sternal ribs ; and a pair from the pelvis, to which is attached false 

 floating ribs, or a pair of those that articulate with the hinder borders 

 of the preceding sternal pair proper. 



In Ardea hfrodias and A. candidissima, the second pair of free ribs 

 support epipleural appendages, low down on the bone. 



For the moment I must now be permitted to defer our further con- 

 sideration of the vertebral column, until the sternum and pectoral arch 

 have been disposed of. After that I will return to the examination of 

 the pelvis and coccygeal vertebrae, upon the completion of which the 

 appendicular skeleton will finally engage our attention. 



Of the Sternunt. — (Figs. 7, 8, 9, 31, and 32.) Upon direct jjec- 

 toral view, the sternum of Ardea herodias is seen to be broader in front 

 than it is behind ; this is due to the projection from the former end 

 of the large costal processes on either side, or otherwise the bone on 

 this aspect would have a nearly regular quadrilateral figure. 



The xiphoidal extremity is doubly notched — a broad triangular in- 

 dentation deeply entering upon either side. This gives rise to outer 

 xiphoidal processes, each of which point directly backwards, and 

 have simply rounded extremities. 



