BRAIN AND NERVOUS SYSTEM 153 



the owls (4 to 7) and in the goatsuckers ; this might lead, in 

 connection with the total absence of the pecten in Apteryx, 

 to the conclusion that the less or greater development of the 

 organ had some relation to nocturnal or diurnal habits. 

 But the existence of only four in the emu seems to throw 

 some doubt upon this suggestion. Among the passerine 

 birds the largest number (raven 30) of folds in the pecten 

 is found. 



Certain small ossifications in the cornea near to the 

 entrance of the optic nerve seem to be peculiar to the 

 Passeres and to certain picarian birds. The eyes have both 

 lacrymal and Harderian gland ; the eyeball is moved by four 

 recti and two oblique muscles ; the membrana by two 

 muscles, the quadratus and the^^^/^'aTOtcZaKs, both innervated 

 by the sixth cranial nerve. 



The Ear. — Birds have no external ear (concha), but in 

 many a flap forming a valve projects into the meatus from 

 "the outer niargin, a state of affairs which recalls the condi- 

 tions found in the crocodile. This outer ear is especially 

 well developed in the owls, in which birds also the ear region 

 of the skull is often markedly asymmetrical. 



The inner ear has the three semicircular canals of all 

 higher vertebrates, but the cochlea is not coiled. The audi- 

 tory ossicles consist of a single structure, partly bony and 

 partly cartilaginous, called thte columella. 



The Affinities of Birds 



In considering the relationship of birds to other verte- 

 brates it is probably safe to leave out of consideration the 

 mammalia and the amphibia. Points of likeness have, it is 

 true, been urged in favour of the latter view of an affinity 

 between birds and amphibia by the late Professor Parkee ; 

 but apart from warm-bloodedness and the resemblance 

 of some of the more simple forms of feathers to hairs 

 there is nothing to be said on behalf of a kinship 

 between birds and mammals. As to the likeness with 

 amphibians, it is possible that the divergence of birds from 



