'548 



ZOOLOGY 



SECT. 



Fio. 1139. Dorsal view of brain of Gray's "Whale 



(C'or/ia grai/'t). (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 



eye of Birds and 

 Reptiles is absent. 



In most Mammals 



"~ r "\l'< I' f" ""-^ 4 ?; .1 ,1 



fl -~j- *C^ rjL^^"'' there are three 



m 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- 

 boniian 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 ear 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 

 a ml ito i -i i 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. Bv the 



sn. 



\~~i\ii. 



FIG. 1140. Sagittal section through the nasal and 

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

 the three olfactory ridges formed by the turbinals ; 

 /; entrance to the mouth ; Ig. tongue ; os, open- 

 ing of Eustachiaii tube ; sn', frontal sinus ; s/i", 

 sphenuidal sinus ; r. /, atlas vertebra ; r. it, axis 

 vertebra. (After Wiedersheim.) 



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 

 j>"sstfr/c (Fig. 1141, Ex.). This, the length of which varies, leads in- 



