548 



ZOOLOGY 



SECT. 



FIG. 1139. Dorsal view of brain of Gray's Whale 



(Coyia grayi). (After Haswell.) 



In essential structure the eye of the Mammal resembles that of 

 the Vertebrates in general (see p. 103). The sclerotic is composed 

 of condensed fibrous tissue. The pecten or marsupium of the 



1 eye of Birds and 

 Reptiles is absent. 

 In most Mammals 

 there are three 

 movable eyelids, two, 

 upper and lower, 

 opaque and usually 

 covered with hair, 

 and one anterior, 

 translucent, and hair- 

 less the nictitating 

 membrane. The se- 

 cretions of a lacry- 

 mal, a Harderian 

 and a series of Mei- 

 bomian glands moisten and lubricate the surface of the eye-ball 

 and its lids. In Moles, and certain other burrowing Insectivores 

 and Rodents, and in Notoryctes among the Marsupials, the eyes 

 are imperfectly developed 

 and functionless. 



The car of a Mammal 

 is more highly developed 

 than that of other Verte- 

 brates, both in respect of 

 the greater complexity of 

 the essential part the 

 membranous labyrinth 

 and in the greater develop- 

 ment of the accessory 

 parts. A large external 

 auditory pinna, supported 

 by cartilage, is almost in- 

 variably present, except in 

 the Monotremata, Cetacea, 

 and Sirenia. This is a 

 widely open funnel, of a 

 variety of shapes in differ- 

 ent groups, having the 

 function of collecting the 

 waves of sound. By the 

 action of a system of 



muscles it is capable of being turned about in different directions. 

 Enclosed by its basal part is the opening of the external auditory 

 passage (Fig. 114?, Ex.). This, the length of which varies, leads in- 



-v.t. 



FIG. 1140. Sagittal section through the nasal and 

 buccal cavities of the human head. /, //, ///, 

 the three olfactory ridges formed by the turbinals ; 

 1>c, entrance to the mouth ; Ig. tongue ; os, open- 

 ing of Eustachian tube; sn', frontal sinus; sn", 

 sphenoidal sinus ; r. i, atlas vertebra ; r. ii, axis 

 vertebra. (After Wiedersheim.) 



