422 THE ANATOMY OP VEETEBEATED ANIMALS. 



dyloid foramen opens into a fossa common to it and the 

 foramen lacerum posticum. All have a short ccecum. The 

 penis is small, and its bone small, in-egular, or absent. 

 They have Cowper's glands and a well-developed prostate. 



The Cynoidea are all digitigrade, and resemble the Dog 

 in their dentition. The Arctoidea are plantigrade, while 

 the Ailuroidea are for the most part digitigrade, bxit may be 

 plantigrade. In dentition, each of these groups presents 

 forms such as the Bears on the one hand, and the Oats on 

 the other, which may be regarded as extreme modifications, 

 in opposite directions, of the type exhibited by the Dog. 



In the Bears, the dental formula is the same as in the 

 Dogs, but the crowns of the teeth are all more obtuse. The 

 sectorial teeth lose their marked characters, and the molars 

 have flat and tiiberculated crowns. The anterior pre- 

 molars fall out as age advances. It is a remarkable cir- 

 cumstance that the teeth of fragivorous and carnivorous 

 Bears exhibit no such differences as would lead to a sus- 

 picion of their complete difference of habit, if we were 

 acquainted with these animals only in the condition of fossils. 



The Cats have the dental formula i. — c. -— ».m. — 



3-3 1—1 r-""- 2-2 



'". j-^j = 30. The canines are very long and sharp. The 



premolars are like the Dogs', except that they are sharper, 

 and that the hindermost (the sectorial tooth) has hardly 

 any internal process. The single upper molar is a small 

 tooth with a flat transversely elongated crown, and it lies 

 within, as well as behind, the great sectorial premolar. In 

 the lower jaw, the sectorial, or first, molar is the last 

 tooth in the series. The crown is a deeply bifurcated blade 

 representing the antero-external cusp of the corresponding 

 tooth in the Dog. The " heel" is obsolete. 



While the Bears are among the most completely planti- 

 grade of the Camivora, the Cats are most entirely digiti- 

 gi-ade, and the apparatus for the retraction of the ungual 

 phalanges is so well developed that the claws are com- 

 pletely retracted within sheaths of the integument, when 

 the animal does not desire to use them. To this end the 



