OF THE CLASS MAMMALIA. 



15 



of bone. Besides these more general characters by which the 

 Lissencephala, in common with the Lyencephala, resemble Birds 

 and Reptiles, there are many other remarkable indications of their 

 affinity to the Oviparous Yertebrata in particular orders or genera 



Fig. 2. — Brain of Beaver. 



Tie;. 1. — ^Brain of Opossum. 



of the subclass. Such, e.g.^ are the cloaca, convoluted trachea, 

 supernumerary cervical vertebrae and their floating ribs, in the 

 3-toed Sloth ; the irritability of the muscular fibre, and persistence 

 of contractile power in the Sloths and some other Bruta ; the long, 

 slender, beak-like edentulous jaws and gizzard of the Anteaters ; 

 the imbricated scales of the equally edentulous Pangolins, which 

 have both gizzard and gastric glands like the proventricular ones 

 in birds ; the dermal bony armour of the Armadillos like that of 

 loricated Saurians ; the quills of the Porcupine and Hedgehog ; 

 the proventriculus of the Dormouse and Beaver ; the prevalence 

 of disproportionate development of the hind-limbs in the Bodentia ; 

 coupled, in the Jerboa, with confluence of the three chief meta- 

 tarsals into one bone, as in birds ; the keeled sternum and wings 

 of the Bats ; the aptitude of the Cheiroptera, Insectivora, and 

 certain jRodentia to fall, like E/cptiles, into a state of true torpidity, 

 associated with a corresponding faculty of the heart to circulate 

 carbonized or black blood : — these, and the like indications of co- 

 affinity with the Lyencephala to the Oviparous air-breathing 

 Vertebrata, have mainly prevailed with me against an acquiescence 



