102 SuvF-EhDT, Osteology of Harris's Cormoyant. [,st'^"oct 



that the bone is very thin at the bases — so thin, indeed, that in 

 some sterna the light can be readily perceived through it when 

 the bone is properly held up to the sun or a flame (No. 19,720). 



After quitting the haemapophysial facets and their indentations, 

 the lateral borders of the bone become sharp and thin, remaining 

 so to their terminations. 



Posteriorly, the xiphoidal border of the bone, in all Cormorants' 

 sterna examined by me, present a somewhat broad, mesial) y 

 notched, middle projection ; at either postero-external angle a 

 somewhat longer and narrower prolongation, while the so-called 

 " notches " — one on either side — between them are rnoderatelv 

 profound on^y, and sub-circular in outhne (fig. 7, Plate XVI.) 



In some specimens of Harris's Cormorant this pattern of its 

 xiphoidal border exhibits some indications of absorption, as a 

 shallowing of the " notches," and a disappearance of a part of 

 the median prolongation. 



All Cormorants have the dorsal aspect of the sternum very 

 smooth, while a raised, rounded ridge passes backward from 

 either costal border to meet, and merge completely, in the median 

 plane posteriorly {P. auritus, P. urile, &c.) This is also found 

 in Nannopternm, but is far more feebly marked ; and in this bird, 

 where the xiphoidal part of the bone begins to exhibit evidences 

 of disappearance, this ridge behind has already disappeared. 

 This is the case in all specimens now at hand. 



Ventrally, the sternum of Harris's Cormorant is likewise smooth, 

 its areas for muscular insertion having been reduced to a limited 

 triangular area, bounded by a raised ridge on either side of the 

 rudimentary carina. These concavities vary in different speci- 

 mens with respect to their distinctness or depth. They do not 

 show well in fig. ig, for example, for they are to some extent 

 shallow in the sternum of that individual — in fact, the sternum 

 of that bird has its " body " very thin in some places — so thin, 

 indeed, that in one place a vacuity is formed, as may be noted 

 in the round spot in the figure.* 



One of the most interesting features to be noticed with respect 

 to the sternum of Harris's Cormorant is its anterior border. 

 Here, the middle and above this is occupied by a rather deep, 

 broad, and uniformly concave notch, with its concavity directed 

 upward. This occurs just above the thick and shallow remains 

 of the anterior border of the rudimentary keel, which is fashioned 

 after the articulatory support of the os fnrcida. Far apart, and 

 on either side, is foimd a deep, well-marked coracoidal groove, 

 these being quite as much in evidence as they are on the sterna 



* The foramen in question might be taken for a shot-hole, but it is not, 

 for its edges are sharp, clean, and unbroken. Two of the sterna of this 

 Cormorant at hand have shot-holes in them — that is. No. 19,721, which 

 received four, and No. 10,719, which has one. These all show the un- 

 mistakable diagnostic evidences or signs of gunshot perforations through 

 an osseous plate, and are very different from such openings as are due to 

 deficient ossification. 



