580 



ZOOLOGY 



SKCT 



Fir:. 1207.- 



-Braiii of Kangaroo {Macropim 

 iiiajor). (After Owen.) 



smooth, or nearly smooth, surfaces. In the hi^lier types tlie 

 relative development of tlie hemispheres is immense, and their 

 backward extension causes them to cover over all the rest of the 



brain, while the cortex is thrown 

 into numerous complicated con- 

 volutions separated by deep 

 sulci (Fig. 1208). This develop- 

 ment of the cerebral hemispheres 

 reaches its maximum in Man. 



The organs of special sense 

 have the same general structure 

 and arrangement as in the 

 Sauropsida. JncoJ>so/is organs, 

 which in the Sauropsida consti- 

 tute such important accessory 

 parts to the olfactory apparatus, 

 are well developed only in the 

 lower groups of Mammals. Tlie 

 olfactory mucous membrane is of 

 great extent, owing to the de- 

 velopment of the convoluted 

 ethmo-turbinal bones over which 

 it extends. In the toothed 

 Cetacea alone among Mammals 

 do the nasal chambers lose their sensory functions— the olfactory 

 nerves being vestigial or absent. The organs of taste are task- 

 li'ds m the mucous membrane covering certain of the papillie 

 on the surface of the tongue. 



In essential structure the ci/c of the Mammal resembles that of 

 the Vertebrates in 

 (see p. 109). 

 sclerotic is com- 

 posed of condensed 

 fibrous tissue. The 

 pecten of the eye of 

 Birds and Reptiles is 

 absent. In most Mam- 

 mals there are three 

 movable eyelids, two, 

 upper and lower, 

 opaque and usually 

 covered with hair, and 

 one anterior, translu- 

 cent, and hair-less — 

 the nictitating membrane. The secretions of a lacrymal a Harderian 

 and a series oUTcibomian glands moisten ami lubricate the surfiice 

 of the eye-ball and its lids. In Moles, and certain other burrowincr 



general 

 The 



Flfi 



120S.— Doreal view of brain of Gray's Whale 

 {Cogiu (jrayi). (After Ilaswell.) 



