84? Dr Treviranus on the 



system, with the natural characters of the famihes for the class 

 of mammalia. 



The proportion of the spinal cord to the encephalon which 

 we have already found of such value in the primary divisions of 

 the vertebrata, is no less important in their further subdivision. 

 I have found it to correspond with, and to follow, analogous gra- 

 dations, with the natural characters in the genera and species. 

 Of these dimensions, the most important are the greatest breadths 

 of the two organs, which agrees with their relative weights, and 

 very nearly with the transverse diameters of the cranial cavities, 

 and of the occipital foramen. In the following table, I have 

 brought together several of these relations, and have ranged the 

 species according to their natural affinities. Those marked with 

 an asterisk are taken from TiedemanTCs Icones Cerebri Simia- 

 mm et quorundam Mammalium Rariorum ; the others are 

 from my own observation. Most of these last depend on im- 

 mediate measurements of the brain and cord. Those marked 

 with a cross, are the relative breadths of the occipital foramen 

 and of the cranial cavity. 



The greatest breadth of the spinal cord immediately behind 

 the pons is to the greatest breadth of the cerebrum, 



In Man, as - - . 100 : 685 



Simla spKinx, - - : 470 



capucina, - - : 430 



• Sabaea, - - : 414 



• Resus, - - : 365 



• Cynomolgus, - : 352 to 360. 



• Nemestrina, - : 357 



• Lemur Mongoz, - : 371 

 f Ursus maritimus, - : 322 



Canis vulpes, - - : 278 



Mustek Foina, - - : 270 to 308 



• Felis Leo, - - : 275 



• Nasua narica, - - : 208 to 248 



• Lotor vulgaris, - - : 248 

 Erinaceus europreus, - : 230 

 Talpa europjea, - - : 200 to 265 

 Vespertilio mjotis, - : 192 

 Didelphis virginiana, - : 147 



• Mus alpinus, - - '• 227 



Rattus, - - : 204 



Cricetus, - - : 205 



• Hystrix cristata, - - : 2C0 



• Castor Fiber, - - : 207 



• Cavia Agouti, - - : 222 

 Lepus timidus, - - s 230 

 Capra ovis, - - : 250 

 Sus Scrofa sinensis, - : 222 



• Phoca vitulina, - - : 362 

 •f Monodon Narwhal, - J 363 



