48 



INTRODUCTION. 



and others, as the ostrich and cassowary, which run with great 

 velocity, employ their short wings to balance their bodies ; but 

 the more ordinary swift-footed birds, as the Plovers and Cur- 

 lews, do not avail themselves of their wings in running. 



On the water, birds are propelled like a boat, by means of 

 their webbed feet, w^hich act alternately in the manner of pad- 

 dles. Those species which dive in pursuit of their prey, propel 

 themselves under water by alternate motions of their feet, but 

 also, and that more especially, by the synchronous action of 

 the wings, which are used precisely in the same manner as in 

 aerial flight, as I have frequently observed. A flock of Red- 

 breasted ^lergansers, in pursuit of sand-eels, in one of the shal- 

 low sandy bays of the Outer Hebrides, has frequently afforded 

 me, from a concealed station on some prominence, a most in- 

 teresting sight. These birds seemed to move under the sur- 

 face with almost as much velocity as in the air, and often rose 

 to breathe at the distance of 200 yards from the spot at which 

 they had dived. 



The Nervous System of birds, which, although less developed 

 than that of some of the mammifera, is greatly superior to that 

 of the other oviparous vertebrate animals, exhibits a remark- 

 able uniformity in the structure and form of the brain and 

 spinal marrow in the different tribes. Figs. 7, 8, and 9, re- 

 present the brain of a sparrow, Passer domesticus, as seen from 

 above, Fig. 7 ; from behind, Fig. 8 ; from beneath, Fig. 9, 



The Brain of a Sparrow. 



Fig. 9. 



6 



Fig. 7. 



In Fig. 7. are seen, besides the bill and part of the skull, ;r, 

 and the eyes, z, the cerebrum, composed of two lobes or hemi- 

 spheres, a, a, which are destitute of convolutions, as well as of 

 the corpus callosum or great commissure ; and the cerebellum, b, 



