540 



CHORDATA 



resulted in an intelligence far superior to that of the reptiles, which finds 

 its expression in the better development of sense organs and brain. In the 

 brain (fig. 592) the cerebellum, the central organ for the coordination 

 of the action of parts, is strikingly developed. The cerebral hemispheres 

 are correspondingly large, the frontal lobes of which begin to cover the 

 olfactory lobes, the temporal lobes in like manner extending back over 

 the 'twixt brain and optic lobes. Corresponding to the vocal apparatus, 



Co- 7 



-H.K. 

 -Kn. 



Tn. 



FIG. 592. FIG. 593. 



FIG. 592. Brain of pigeon (from Wiedersheim). HH, cerebellum; Lol, olfactory 

 lobes; MH, mid brain; NH, medulla oblongata; VH, cerebrum. 



FIG. 593. Eye of owl (after Soemmering and Franz). Ch, chorioid; Cm, ciliary 

 muscle; Co, cornea; Cv, vitreous body; HK, posterior chamber; Jr, iris; Kn, sclerotic 

 bone; L, lens; Op, optic nerve; P, pecten; PC, ciliary process; Rt, retina; Sc, sclera; 

 Tn, tapetum nigrum; FA', anterior chamber. 



the ear is highly organized, the lagena of the labyrinth being greatly en- 

 larged and the sound-conducting apparatus (columella, tympanum, 

 etc.) well developed. The beginnings of an external ear are seen in the 

 deeper position of the drum membrane. Since the power of flight neces- 

 sitates vision at great distances, most birds have exceedingly sharp sight, 

 and the eye itself (fig. 593) has a special apparatus (Crampton's muscle) 

 for different distances. Peculiarities of the bird's eye, already weakly 

 developed in the reptiles, are the pecten (P), a comb-shaped growth of 

 the chorioid into the vitreous body, the scleral ring, a circle of bones 

 developed in the sclera and supporting the outer part of the eye, and a 

 nictitating membrane besides the ordinary eyelids. 



Among birds there is spirited rivalry for the females, especially among 

 polygamous species. At the time of mating the males seek to win the favor of 

 the females either through striking motions (dances), by singing, or by beauty 

 of plumage. All of these peculiarities are confined to the male and frequently 

 lead to a marked sexual dimorphism. The distinction in plumage is commonly 

 strengthened at this time, the male receiving the brilliant wedding dress. 



