THE DOMESTIC PIGEON 371 



composed of a pair of narrow scapulas (Fig. 192, 10), to 

 which are attached two coracoids (Fig. 192, ll), connecting 

 the scapulas and the sternum, and a V-shaped bone, the wish- 

 bone, formed from the union of the two clavicles (Fig. 192, 14). 

 A greatly enlarged sternum with a prominent ridge or keel 

 (Fig. 192, 12) serves as a surface for attachment of the mus- 

 cles of flight. The hip-girdle is united to the vertebrae of 

 the pelvic region (Fig. 192, 7). A study of Fig. 192 and com- 

 parison with the skeleton of the frog (Fig. 165) will make 

 clear in what respects the appendages are different. 



The Nervous and Muscular Systems. The brain is larger 

 in the pigeon, in proportion to the size of the animal, than 

 in the amphibians and reptiles. The cerebrum (Fig. 191, 44) 

 and the cerebellum (Fig. 191, 46) are especially large. One 

 of the principal functions of the cerebellum is to control the 

 muscles which bring about the balancing of the body. It is 

 apparent that this is of greater importance in the birds and 

 fishes than in the broader-bodied amphibians and reptiles. 

 The optic lobes (Fig. 191, 45), pressed to one side by the large 

 cerebrum, are also well-marked, in correlation with the 

 unusually large eyes and the dependence of the pigeon on 

 the sense of sight. The, olfactory lobes (Fig. 191, 42) are rela- 

 tively small, and the sense of smell is not at all keen. The 

 medulla (Fig. 191, 47) is bent downwards, as in the reptiles. 



The muscular system shows many adaptations to the aerial 

 life of the pigeon. The great mass of muscle by which the 

 downward stroke of the wings is accomplished, occupies 

 almost all the space on the prominent, keeled breast-bone. 

 Its position, low down on the body, makes overturning in 

 the air almost an impossibility. The muscle which raises the 

 wing is also situated beneath the breast-bone, and is inserted 

 on the dorsal surface of the humerus by a tendon which 

 passes through an opening at the shoulder. The tendon thus 

 acts as a pulley in raising the wing. The muscles which 



