No. 445 ] OSTHOLOGV OF PVGOPODES. 



37 



so anteriorly and o-radualh shallowin-- as \w approach its hinder 

 part. Both this surtacc and the \cntral one are \ery sinootli. 

 Upon the latter the • pectoral nuiseular hne ' extends 'trom the 

 mid point of the lower lip of the outer third of the costal ,-roove 

 obliquely to the carina meetin,i4 it at the juncture of its anterior 

 and middle thirds. In I', /w/r/- the Ixme averages jocentime- 



[jrocesses. Though very light and ele-antly proportioned the 

 base is absolutely non-pneumatic throu.^hout the su])ertainily. 

 Its form is well shown in the sternum of I'rntator luinnic (.Spec. 

 No. 16628 of the U. S. Xat. Mus. Coll. 9 ) hut its pattern may 

 vary considerably, being remarkably narrow and long in some 

 individuals. When thus fashioned it reminds one ver\- nnich of 

 the sternum in certain of the auks. But among some water birds 

 skeletal characters crop out very strangely sometimes, and even 

 to the casual observer the sternum of an albatross, a cormorant, 

 Plotus, a fulmar, and a grebe all more or less closely resemble 

 each other upon a direct pectoral view, and to a less extent in 

 several of those forms, when viewetl from the side. 



says: " X'iewing. now, the sternum as a uhok-. we ha\e to 

 notice how great an extent of surface is sec ured with a trifling 

 increase of weight. Posteriorly, this is attained by me;ms of the 

 great lateral projection of the apophyses, as well as by their 

 length, and by the breadth and projection backwards of the thin, 



not so wide, the deficiency is atoned for by the great depth of 

 the keel, and its projection forward; at the same time the out- 

 line of the crest of the keel is such that when the inequalities 

 of the bone is all filled up with muscular tissue the resulting 

 surface becomes flat, and broad as well as long, affording the 

 best possible outline for contact with the water." {loc. cit. })p. 

 147, 148.) 



According to Marsh ''The sternum in Ihspcroniis somewhat 



