If) CLASS MAMMALIA. 



of the body. Sometimes these amount to actual prickles, 

 very stiff and hard, and it is probable, that the muscles of 

 the skin have some modification enabling them to raise 

 these prickles ; but this is a point not clearly ascertained. 



The tongue, in some species, is very soft ; in others 

 slightly papillated. 



The eyes are somewhat variable in size, and this, as in 

 the other Mammalia, is determined by the habits to which 

 the animal is destined. They are small, for instance, when 

 the animal burrows in the earth, or lives in the water. In 

 some of the aquatic species, as the Ornithorhyncus for 

 example, the crystalline is very convex. As to the rest, 

 they have the essential characters of Mammalia, as to the 

 disposition of the internal lid, and that of the straight and 

 oblique muscles, fyc. 



It would seem to be otherwise with the organ of hearing, 

 if what Sir Everard Home advances concerning there being 

 but two small bones in this organ in the Ornithorhyncus be 

 correct. As to the other Didelphes, they have certainly 

 three or four, and the general apparatus of this sense is 

 altogether similar to that of the ordinary Mammalia ; simi- 

 lar modifications under similar circumstances, as the ab- 

 sence of a conch when the animal is aquatic or subterra- 

 neous. 



If we find really no material differences in the organs of 

 sense in the Marsupiata from other animals, this is by no 

 means the case with the organs of loco-motion : there are 

 some very remarkable ones in the skeleton, though not in 

 all its parts. Thus, the general form of the vertebras in 

 the different portions of the vertebral columns, that of the 

 head, or cranium, have nothing different from the common 

 Mammalia. The classic characters are also to be found in 

 the articulation of their bodies, in the form of the articular 

 and transverse apophyses. The cervical vertebras are pretty 



