4()0 MR. A. H. GARROD ON THE [Mlty 6, 



Meckel, Nitzsch, and Owen stating that there is only a right carotid 

 in Phcenicopterus. I have had the opportunity of examining two 

 specimens of Phcenicopterus antiquonim and two of P. ruber ; and 

 in all of them both carotids were present in the lower part of the 

 neck, the right being much the larger and being joined by the left 

 to form one trunk at the point in the neck where they first meet, as 

 in Botaurus stellaris. Both vessels carried blood ; but the calibre of 

 the left was extremely small, and that of the right was nearly the 

 same as it would have been if it alone bad been present. 



From the list at the end of this paper it is shown that of 300 

 genera in which the arrangement of the carotids has been ob- 

 served, in 193 of them both are present, in 107 the left only ; in one 

 only are both equal wheu they join in the neck ; in another they 

 join, the left being the smaller ; and in one other the right is the 

 smaller under similar conditions ; whilst perhaps one possesses the 

 right onlv. So it may be generally stated that in birds either both 

 carotids "are present separate, or the left only exists. Several at- 

 tempts have been made by different authors to account for these 

 peculiarities. According to Bauer, the simplicity of the carotids (in 

 other words, the presence of the left instead of two) is dependent on 

 the size of the individual, the smaller species having the single trunk. 

 Undoubtedly the great majority conform to this rule ; but there are 

 too many exceptions, as shown by Meckel, to make the generaliza- 

 tion of much value, Rhea, Podiceps, Cacatua, Taleyalla, and Me- 

 nura possessing only the left. Meckel originally thought that a 

 correlation existed between the length of the neck and the sim- 

 plicity of the carotids ; but when he found two carotids in Struthio, 

 Dromceus, Cygnus, and Ardea he acknowledged that such was not 

 the case. Prof. Owen remarks*, " Birds as a rule are peculiar in 

 sleeping with their long necks much bent or twisted ; and this posi- 

 tion might he expected to exercise some effect on the vessels subject 

 thereto. Accordingly we find that the carotids are frequently of 

 unequal size; in the Dabchickf the left is the largest; in an Emu 

 I found it the smallest." I may here remark that on several occa- 

 sions I have watched the Flamingos sleeping ; and they do so, some 

 with the neck bent one way and some the other, in a manner quite 

 independent of the constant peculiarity in the arteries of their 

 necks. 



All these explanations, therefore, fail to show why birds should have 

 two or only one carotid artery ; and it is the last of them only that 

 takes into consideration which carotid would be absent when there is 

 any deficiency. If it were proved that all birds with a left carotid 

 slept with their necks bent in one direction, the only explanation 

 would be, that they did so because the arrangement of their cervical 

 vessels would not allow of their doing otherwise, and consequently an 

 argument in a circle would be the only result. The ultimate cause is 

 most probably as yet some way beyond our grasp ; but I would offer 



* Anatomy of Vcrtebrata, vol. ii. p. 190. 



t In the Grebes {Podiceps), according to my observations, the right carotid is 

 not found to be present at all. A. H. G. 



