1890.] ANATOMY OF PODICA SENEGALENSIS/ 441 



to oue organ or system, but are manifested in the entire structure — 

 bones, muscles, and viscera. 



It appears to me, therefore, to be necessary to strongly emphasize 

 the justice of regarding the Heliormtliidm as a distinct and well- 

 marked family. The following is a brief definition of that family : — 



Characters of the Family Heliornithidte. 



Schizognathous holorhinal birds with 18 rectrices, moderately 

 long caeca, a tufted oil-gland, no aftershaft ; with an elongated one- 

 notched sternum and low carina ; clavicles with an anterior and 

 posterior interclavicular process, the latter firmly attached to the 

 carina sterni ; the skull without basipterygoid processes, occipital 

 foramina and supraorbital furrows, and without greatly developed 

 temporal fossae. Biceps slip ending freely on patagial membrane ; 

 expansor secundariorum weU developed; in the hind limb ambiens, 

 femoro-caudal, accessory femoro-caudal, semitendinosus present, 

 accessory semitendinosus absent ; relations of biceps cruris peculiar. 

 Muscular formula of leg ABX-|-. 



Affinities of the Heliomithidae. 



It is curious to notice that the osteological characters and those 

 shown by the muscles are almost in antagonism. 



Judged entirely by its myology, Podica would be referred to the 

 Pygopodes, though it would doubtless be regarded as an aberrant 

 member of that group \ 



If only osteology were taken into consideration, then Podica would 

 be as unhesitatingly assigned to the Rails, though the characters 

 afforded by the sternum would necessitate its separation as a very 

 distinct genus from the other Rail-like birds. 



"Which set of characters are we to be guided by in attempting to 

 settle the systematic position of the Heliornithidce ? 



It is hardly necessary to emphasize the fact that in deducing 

 affinities one character is not as good as another ; adaptive characters 

 must clearly be set aside when they are not in harmony with 

 structural characters showing no evident relation to the mode of life 

 of the bird. 



I should be inclined therefore, in the first place, to discount very 

 liberally the skull characters, as least some of them. 



The strongly developed temporal fossee with the ridges on either 

 side of them distinguish the Grebes from the Rallidce. But we find 

 exactly the same extraordinaril)' developed fossae in the Ardeidce and 

 in Plotus and Phalacrocorax. These birds, like the Grebes, use their 

 neck and heads greatly and have ijowerful muscles which are inserted 



'^ This makes me think that Mr. Forbes must have dissected Podica or Pocloa; 

 otherwise, if he had only published accounts to go upon, or had only examined 

 the osteological structure, he would hardly have definitely placed it in tlie same 

 group with the Divers and Grebes, as he did at the close of his career [12]- 



