292 FOOT AND ACTION 



equal sides, of which the outer toe (which is generally 

 very long) and the back one form the largest diameter. 

 This is articulated upon the tarsus, intermediate be- 

 tween the directions of inward and forward, as may 

 be seen in the annexed cut of the foot of the gannet, 

 which, as one of the most active and best known 

 birds of the group, may be taken as the type, in as 

 far as the foot is concerned. 



The birds which have this structure of foot are all 

 fishers, and most of them (the gannets especially) 

 dash down almost perpendicularly from great heights 

 upon their prey, and seize it with the bill. The gan- 

 net is curiously provided against any injurious effect 

 from these headlong plunges. On the breast and 

 throat of this bird there are three great air-cells 

 between the integuments and the muscles, the two 

 largest divided (but not shut out) from each other by 

 a perforated septum along the keel of the sternum, 

 and tied to the enveloping membrane of the muscles 

 by a number of small straps of membrane ; and the 

 smaller one anterior of the furcal bone, and not com- 

 municating with the other two, though all the three 

 have communications with the air-cells in the interior 

 of the bird. When the bird dashes down at a fish, 



