149 



still do not cover either the olfactory lolies in front, or the cere- 

 bellum behind. The corpus coUosum or cerebral commissure is present 

 in the brains of this order. The foregoing peculiarities, and especially the 

 smooth surface of the cerebral lobes, have induced Professor Owen to make a 

 subclass of the four orders, Bruta, Cheiroptera, Insectivora and Rodeutia, 

 imder the name of Lissencephala, or Smooth-brains. Although there e.\ists 

 without doubt a great deal of similarity between the brains of these four orders 

 of Mammalia, yet as many other distinctions are found between them, as well 

 as a considerable diversity in the formation of their brains. Professor Owen's 

 classification is not generally followed. At the same time, however, it ia 

 universally admitted that the four orders, Bruta or Sloths, Cheiroptera or 

 Bats, Insectivora Shrews, Mole, &c., and Rodentia, Rats, Rabbits, &c., are 

 closely allied together in a classificatory point of view. The foregoing 

 account of the brain of Rodentia will point to a somewhat low amount of 

 intelligence among these animals ; we find, however, that in some instances 

 their social instincts (as in the beaver) rise to a great perfection. Like most 

 small Mammals the Rodentia have a wide geographical distribution, and are 

 exceedingly prolific. Some members of the order are found in nearly every 

 known part of the globe, and several species have an immense range. Thus 

 the brown or common rat has dispersed itself with man, over the whole of 

 the inhabited portion of the world ; it is believed to have come originally from 

 the East. The common mouse is also found almost everywhere that the 

 human race have settled. The Beaver has a range over the northern parts cjf 

 Europe, Asia, and America, and was once an inhabitant of this country. The 

 Musk Rat is a native of Northern America ; The Beaver Rat, or Hydromj'e, 

 of Van Dieman's Land. The Porcupine inhabits Southern Europe, Africa, 

 and India. The Urson, which is an animal much resembling the Sloths, is a 

 native of Canada, and lives upon the trees. South America is also repre- 

 sented by the Guinea pig, the Capybara, the Agouti, and the Chinchilla ; 

 Africa by the Gerboas, or leaping Hares. 



I will pass on now from this brief notice of the distribution of this order 

 to notice shortly the British species of the order. The following may be 

 regarded as natives of this country : — 



Hare— Lepus timidus. 

 Rabbit — Lepus cuniculus. 

 Dormouse — Myoxus avellanarius 

 Spuirrel — Sciurus Europoeus, and 

 Formerly the Beaver— Castor fiber. 



Brown Rat — Musdecumanus. 

 Black Rat — Mus rattus. 

 Common Mouse — Mus musculus. 

 Harvest Mouse — Mus sylvaticus. 

 Water Vole — Arvicola amphibius. 

 Campagnol — Arvicola arvalis. 



The common, or brown rat, is an animal too weU known to need minute 

 description, and its dental formula is similar to that found throughout the 

 order. It is supposed to have been imported into this country not much 

 more than a century ago, but it is so fierce and so prolific that it has 



