•)ftO 



ZOOLOGY 



Fin. l-jiiT.— lii-ain of Kangaroo (A/i 

 „H,j(if). (AftuvOwcii.) 



smooth, or nearly smooth, surfaces. In the liiglier types the 

 relative developineiit of tlio 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. JacoJison's 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. The 

 olfactory imccous meviirane is of 

 great extent, owing to the de- 

 velopment of the convoluted 

 ethrao-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 tci^i- 

 Jiiid.'i in the mucous membrane covering certain of the papilla' 

 on the surface of the tongue. 



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

 the Vertebrates in 

 general (see p. 109). 

 The sclerotic is com- 

 posed of condensed 

 fibrous tissue. The 

 ])ecten of the eye of 

 Birds and Reptiles is 

 absent. In most Mam- 

 mals there are three 

 mo\'able eyelids, two, 

 u p per and 1 o w e r, 

 opaijue and usually 

 covered with hair, and 

 one anterior, translu- 

 cent, and hair-less — 

 the mcUtatinr/ memhranc. The secretions of a Incrymril, a Hardcrian 

 and a series oi Mctlmaiiin glands moisten and lubricate the surface 

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



-Iiuv.siil viuw of Iji-aiu .if Gray's VThale 



(C,Hl',il a,;,,,;}. (Aftrr Haswell. ) 



