Chap. IV.] MANNER OF DEVELOPMENT. iif 



smaller, and the convolutions of the brain are less com- 

 plex, than in normal men. The frontal sinus, or the pro- 

 jection over the eyebrows, is largely developed, and the 

 jaws are prognathous to an " effrayant " degree ; so that 

 these idiots somewhat resemble the lower types of man- 

 kind. Their intelligence and most of their mental facul- 

 ties are extremely feeble. They cannot acquire the power 

 of speech, and are wholly incapable of prolonged atten- 

 tion, but are much given to imitation. They are strong 

 and remarkably active, continually gambolling and jump- 

 ing about, and making grimaces. They often ascend 

 stairs on all-fours ; and are curiously fond of climbing up 

 furniture or trees. We are thus reminded of the delight 

 shown by almost all boys in climbing trees ; and this 

 again reminds us how lambs and kids, originally alpine 

 animals, delight to frisk on any hillock, howevei small. 



Reversion. — Many of the cases to be here given might 

 have been introduced under the last heading. Whenever 

 a structure is arrested in its development, but * still con- 

 tinues growing until it closely resembles a corresponding 

 structure in some lower and adult member of the same 

 group, we may in one sense consider it as a case of rever- 

 sion. The lower members in a group give us some idea 

 how the common progenitor of the group was probably 

 constructed ; and it is hardly credible that a part arrested 

 at an early phase of embryonic development should be 

 enabled to continue growing so as ultimately to perform 

 its proper function, unless it had acquired this power of 

 continued growth during some earlier state of existence, 

 when the present exceptional or arrested structure was 

 normal. The simple brain of a microcephalous idiot, in as 

 far as it resembles that of an ape, may in this sense be 

 said to offer a case of reversion. There are other cases 

 which come more strictly under our present heading of 



