161 



a few years since by Mr. M. C. Read, of Hudson, Ohio, that they appeared 

 to be increasing in numbairs. Dr. Kirtland, in his catalogue (1838) gives 

 it as rare. 



— Two other Hares, Lepus palustris and aquaticus, are in one place ac- 

 credited to Ohio by Mr. Allen (Mon. N. A. Rodentia, p. 276), as follows : 

 " These species extend northward over the lowlands of the Lower Mis- 

 sissippi, having been found as far north as southern Ohio." As he in no 

 other place or manner refers to either of them as Ohioan, it is probable 

 that " southern Ohio " should read " southern Illinois." 



SUB-CLASS DIDELPHIA. 

 ORDER MARSUPIALIA. 



These are implacental mammals, which are born of small size and im- 

 perfect development. They are transferred by the mother to the interior 

 of the marsupial pouch or bag, which is present in most species. 



This pouch cons sts of a fold of the abdominaL integument, which, in 

 the males, is everted, forming a pendulous bag containing the testes, 

 and, in the females, is inverted, forming a hidden pouch containing the 

 nipples, and usually sheltering the young for a certain period after their 

 birth. The young are attached to the teats, which grow from the upper 

 surface of the pouch, and are sustained by milk which is forced down 

 the throat of the young by the contraction of the cremaster muscle, 

 which is largely developed and extended over the surface of the mam- 

 mary glands. The teat exactly fills the mouth. The danger of suffoca- 

 tion is averted by the elongation of the upper extremity of the larynx, 

 which is embraced by the soft palate, as in the cetaceans, thus allowing 

 respiration to go on freely, while the milk passes on each side of the 

 laryngeal cone into the oesophagus. 



The pelvis of both sexes is furnished with two characteristic supple- 

 mental bones— ossa marsupinlia. These are elongated, flattened, and more 

 or less curved bones, of the sesamoid series, developed in that tendon of 

 the external oblique which forms the mesial pillar of the abdominal ring. 

 These bones are attached to the pubis ; they are directed forward, and are 

 so long that the cremaster muscle winds round them in its passage to the 

 testicle or mammary gland. The marsupial bones are equally developed 

 in both sexes; their position and attachment add power to the com- 

 pressing action of the cremaster muscle ; they also give origin to the 

 pyramidali"? muscle. The cerebral hemispheres are chiefly connected by 

 a large anterior commissure, the corpus callosum being rudimentary. 



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