540 



CHORDATA 



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

 its expression in the lietter (,le\-elopnient of sense organs and brain. In the 

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

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

 are corresponcUnglv large, the frontal lolies of which begin to cover the 

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

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



Fig. 59;. Fig. 503. 



Fig. 50:?. — Brain of pigeon (from Wiedersheim). HH. cerebellum; Lot, olfactorj- 

 lobes; MH, mid brain; XH, medulla oblongata: VH, cerebrum. 



Fig. 503. — Eye of owl (after Soemmering and FranzV c7j. chorioid; c~«!, ciliar>' 

 muscle: Co, cornea; C""-, \'itreous body; HK^ posterior chamber: Jr, iris: Kn, sclerotic 

 bone: L, lens: Op, optic ner\"e: P, pecten; Pc, ciliar}' process; Rt, retina; 5c, sclera; 

 Tn, tapetum nigrum; FA', anterior chamber. 



the ear is highly organized, the lagena of the labyrinth lieing 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 llight neces- 

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

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

 for different distances. Peculiarities of the bird's eve, alreadv weaklv 

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

 the chorioid into the vitreous l)ody, 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 sjiccics. 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 dimoqihism. The distinction in plumage is commonly 

 strengthened at this time, the male reeei\ing the brilliant wedding dress. 



