A. 



Sauropsida: Class Aves 



B. „„ ffff 



535 



Fig. 416. Brain of pigeon. (A) Dorsal view. (B) Lateral view. (Hyp) Hypophy- 

 sis; (Jnf) infundibulum; (L. ol.) olfactory lobes; (HH) cerebellum; (Med) spinal 

 cord (medulla spinalis); (MH) optic lobes; (NH) medulla oblongata; (Tr. opt) 

 optic tract; (VH) cerebral hemispheres; (I-XII) cranial nerves; (1, 2) first and 

 second spinal nerves. (Courtesy, Wiedersheim : "Grundriss der vergleichenden 

 Anatomie der Wirbeltiere," Jena, Gustav Fischer.) 



more fibers in the optic nerve and the greater the number of nervous 

 elements in the optic centers of the brain. The extraordinarily large 

 eyes of the bird are associated with large optic lobes. 



The all-important function of the cerebellum is the coordination 

 of the activities of the complex sets of muscles involved in locomotion 

 and in maintaining bodily equilibrium — balancing, posture. This co- 

 ordination depends upon stimuli received by the various sense-organs, 

 especially important being those received by the eyes and by the 

 equilibratory organs (semicircular canals) of the ears. Each type of 

 sensory organ has its corresponding primary sensory center in the brain 

 — smell in the forebrain; sight in the midbrain (optic lobes); equilib- 

 rium and hearing, taste, and the various integumentary senses in the 

 hindbrain. Therefore, from these several primary sensory centers, 

 nervous impulses must be relayed into the cerebellum along connecting 

 tracts of nerve-fibers. The muscular activities concerned in flight are 

 of a peculiarly complex sort and require, for their precise coordination, 

 a correspondingly complex nervous mechanism. The cerebellum, how- 

 ever, merely coordinates these activities. Whether or not flight shall 

 occur, its direction and speed, and, in short, the whole pattern of the 

 animal's activities, are determined within nervous centers situated 

 elsewhere in the brain and, for the most part, in regions anterior to the 



