192 INTRODUCTION. 



is observable in the almost bird-like condition of the brain, a part of the 

 animal frame important to be considered, in attempting to form an esti- 

 mate of the rank of groups among the class Mammalia. In accord- 

 ance with the low structural ratio of the brain, is the ratio of their in- 

 telligence. We may tame them, it is true ; but they will not obey the 

 voice of their keeper ; we may tame them, but we cannot educate them. 

 The structural inferiority of the rodents is not displayed by the brain 

 alone : the rudimentary condition of the skull the original parts of the 

 bones, which compose it, remaining distinct, as if by an arrest of ossi- 

 fication, also attests the fact.* Not only is the cranium depressed below 

 the facial portion, but the position of the orbits, with their lateral aspect, 

 is anterior to the cranial cavity ; and often, by the imperfection, or 

 narrowness, of the septum, dividing between them internally, as in the 

 Hares, do they remind us of the orbits of a bird ; even in the Beaver, 

 where they are separated by the nasal cavity, a probe may be passed at 

 the bottom of the orbitar recess (above the alveoli of the molar teeth), 

 through the foramina, from one cavity to the opposite, without entering 

 that of the cranium, or of the nose. 



The comparatively contracted volume of the thorax, the general feeble- 

 ness of the skeleton, and even the number and characters of the teeth, 

 which consist only of molars, and two incisors, indicate a typical inferiority. 

 " En un mot," to use the words of Cuvier, " 1'inferiorite de ces animaux 

 se montre dans la plupart des details de leur organisation." It is true, that 

 the rodents are unguiculate ; that many use their paws with a certain share 

 of address, and, consequently, that many, or most, are claviculated : but, 

 be it observed, that the possession of clavicles, and digitated paws, is a 

 circumstance, in itself, by no means indicative of elevation in the rank of 

 being : other qualifications are requisite ; for it is evident, that animals 

 having instincts leading them to choose the trees for their abode, must be 

 fitted for climbing ; and that animals whose instincts lead them to burrow, 

 must have their organs adapted for excavating the ground ; but the pos- 

 session of these instruments confers, in itself, no positive superiority. 

 When the intelligence of an animal is developed, involving habits in unison 

 with its intelligence, and an according modification of the structure in the 

 extremities, then this organization becomes the index of superiority, in a 

 given sense, but is not the true cause of superiority. We are, indeed, 

 too apt to look upon structural adaptation as the cause of superiority, or 

 of differences in habits and manners ; and, because we are accustomed to see 

 certain modes of structure combined with a superiority in the scale of 

 being, to mistake the result for the cause ; but it ought not to be forgotten, 

 that the modification of organs does not influence habits : habits are the 



* The size of the foramina, for the egress of the nerves, and the magnitude of the nerves, in propor- 

 tion to the volume of the cerebral mass, are remarkable features in the Rodentia. 



