Aves. 217 



kidneys are paired organs, lying embedded in the hollow of 

 the pelvis, each kidney being in three sections. 



The Oil Gland. On the rump, at the base of the tail, is 

 the conical oil gland. It is concealed by feathers, but 

 when the bird wishes to oil the feathers, oil is taken from 

 the gland by the beak and spread over them. The oil 

 glands are the only skin glands possessed by the bird, 

 there being no glands distributed over the skin as in many 

 other animals. 



Nervous System of the Pigeon. The brain is relatively 

 large. It is also wide in proportion to its length as com- 

 pared with the brains of reptiles and amphibians. The 

 anterior part of the brain consists of the two cerebral hemi- 

 spheres (see Fig. 167). Back of these, in the middle 

 line, is the rather large cerebellum, marked by transverse 

 grooves. On the sides of the cerebellum are the two 

 optic lobes. The whole nervous system is relatively large, 

 the brain and spinal cord in some of the smaller birds 

 constituting a greater proportion of the weight than in any 

 other animals. 



The Senses of the Pigeon. Sight is the most highly 

 developed of the bird's senses. The eye is very large in 

 proportion to the size of the head. The outer coat 

 (sclerotic) of the eye is strengthened by stiff sclerotic 

 plates. The sense of sight is keen, enabling the bird to 

 discover food and to escape enemies. 



The sense of hearing is acute, the inner ear being well 

 developed. There is no outer ear, but the depression lead- 

 ing to the tympanum is easily to be found back of the 

 eye, though usually more or less concealed by feathers. The 

 sense of touch is general over the body. Taste is appar- 

 ently not very acute. While it is pretty generally believed 

 that birds, especially carrion eaters, have a keen sense of 



