CHAP. XVI.] SOME OTHER MAMMALS. 279 



proportion to the variety and continuance of the Move- 

 ments which the animal is accustomed to execute. 



Arrangement of Convolutions. In the lowest Quad- 

 rupeds there are no Convolutions at all. This, for 

 instance, is the case with Monotremes, and the lower 

 Marsupials and Eodents. But in other higher forms 

 Convolutions exist, and are arranged in accordance with 

 two distinct types or patterns, which have been named 

 respectively, the ' oblique ' and the * longitudinal.' The 

 following brief references to these two patterns are con- 

 densed from Owen's account of them.* It is not intended 

 to give anything like a full description here, but merely 

 to indicate some of their most striking peculiarities. 



The * oblique pattern ' is met with among the hoofed 

 Quadrupeds, viz., Euminants, Solipedes, and Pachyderms. 

 The ' longitudinal pattern ' pertains to other Mammals, 

 comprised principally within the orders Carnivora and 

 Cetacea. 



A third or ' transverse pattern ' is common to the 

 Quadrumana and Man, as will be shown in subsequent 

 chapters, and on this we shall find it worth while to bestow 

 a much larger amount of attention. 



Notwithstanding the very numerous differences in detail, 

 certain primary ' fissures ' seem to be common to the three 

 types. One of the most constant of these is the ' fissure 

 of Sylvius ' on the outer surface of the Hemispheres ; 

 while, another, also very constant, is the * fissure of the 

 Hippocampus.' The latter, situated on the inner aspect 

 of the hemispheres, has already been alluded to as cor- 

 responding with the body of the same name which 

 projects, in each hemisphere, into a descending pro- 

 longation of the Lateral Ventricle. 



* " Anatomy of the Vertebrates," vol. iii. 



