1892."] 



probably has, though I have not definitely made out the fact, a con- 

 nection with the air-sacs. 



Osteology, and Comparison with Plotns anhinga. 



The osteology of the Darters has received attention from Brandt*, 

 Eyton ^, Donitz ', Garrod ^ and Milne-Edwards*. 



The only one of these authors to describe and figure the species 

 which is the subject of this communication is M. Milne-Edwards. 

 The entire skeleton, as well as the separate bones, are figured in the 

 magnificent work upon the Natural History of Madagascar, now in 

 course of publication. 



Milne-Edwards, however, does not do much more than describe 

 the osteology of P/otus melanogaster ; there is but little in the way 

 of a comparison between this and other species. My ol)ject in the 

 present paper is to point out the principal differences between Plotua 

 melanogaster and P. anhinga. I must first of all refer to an inter- 

 esting matter concerning the skull, which has already been dealt 

 with by Grtrrod for P. anhinga. 



In the figure illustrating the skull ^ Garrod has indicated a small 

 rod (lettered "a") attached to the occipital bone. Of this he 

 wiites as follows : — " In speaking of Phalacrocorax cristatus, 

 Mr. Eyton remarks, the tubercle on the upper edge of the occipital 

 bone has a pointed, movable, triangular process attached to it, which 

 I suspect has also been the case with my specim^i of Plotus, but 

 has been lost." 

 ^ In the Society's female specimen there is a fibro-cartilaglnous, 

 similarly situated process, not more than one sixth of an inch long, 

 which is ossified in the evidently older male. In his notes on the 

 anatomy of the Cormorant, Hunter tells us that "a small bone, 

 about an inch long, passes back from the os occipitis and gives 

 origin to the temporal muscle, which is very strong." The same 

 bone in the Darter, although comparatively not so long, performs 

 the same function, the superficial temporal muscles meeting behind 

 the skull along the median raphe, which becomes ossified to form the 

 above-mentioned bony style in the adult bird." 



This is not figured by Milne-Edwards, but I found the bone in 

 Plotus melanogaster attached precisely as is figured by Garrod for 

 P. anhinga. The bone was of a triangular form, thus resembling 

 more closely the corresponding bone of the Cormorant. It was en- 

 tirt-ly ossified. In comparing the two skulls of P. anhinga and P. me- 

 lanogaster, the process of the occipital bone to which the ossicle in 

 question is attached is seen to have a truncated form in P. melano- 

 gaster, vi\\eri'S\s in P. anhinga it has as Garrod has correctly figured, 

 a more conical form, terminating in a point. 



1 Mem. de I'Acad. Imp. de St. Petersb. t. v. (1839). 

 ^ Osteologia Avium, p. 218. 

 ' Archiv f. Anat. n. Phys. 1873, p. 357. 

 Loo. cit. 



' Histoire nat. de Madagascar, t. xii. p. 690. 

 ^ Loc. cit. pi. xxviii. fig. 1. 



