CHAP. XIII.] THE CATS PLACE IN NATURE. 473 



not in the Carnivora. "With one exception * they always have com- 

 pletely developed clavicles, which in the Carnivora are never more 

 developed than in the cats. Their generative organs may be pro- 

 vided with a sac attached to each vas deferens close to its opening 

 into the urethra, i.e., they may have vesiculse seminales (which 

 Carnivora never have), while the testes are never scrotal, and 

 though the placenta is deciduate it is not zonary. 



Lastly, the Carnivora differ from the PinnijK'dia in that their hind 

 limbs are always more or less well suited for progression on land, 

 being always not only capable of having the plantar surfaces applied 

 to the ground, but also being free and not held together by integu- 

 ment down to the ankles as they are in such Pinnipedia as can 

 apply the soles of the hind feet to the ground, which none of the 

 true seals can do. In these latter the hind legs are permanently 

 stretched out in a line with the axis of the trunk and tied to the 

 tail by a fold of integument, so that they act more like a caudal tin 

 than like legs. Seals are also entirely destitute of an external car 

 or concha. In all the Pinnipedia the middle digit is the shortest in 

 each hind foot. The brain is very large and very much convoluted, 

 and there may be a very small third or posterior cornu to each 

 lateral ventricle, while the olfactory lobes and anterior commissure 

 are rudimentary and the lachrymal canal and bone are absent. 



Altogether it may be said that the cat's order — the Carnivora — 

 differs from all the other Monodelphous mammals put together, 

 in the simultaneous possession of the following common characters, 

 only some of which are possessed by the various other orders : — 



(1) The brain is well developed, with cerebral convolutions (two 



or three around the Sylvian fissure), and a well- developed 

 corpus callosum and small anterior commissure. The 

 cerebral hemispheres do not cover the cerebellum, nor 

 do they contain triradiate lateral ventricles. 



(2) The eyes are well developed, with a choanoid muscle, and 



may have a brilliant tapetum, with an iris capable of con- 

 tracting its aperture to a vertical linear slit. 



(3) The ears are provided with a more or less prominent concha. 



(4) The hyoid has, on each side, a short thyro-hyal and a large, 



segmented, anterior cornu. 



(5) The carpus has a scapho-lunar bone. 



(6) No extremity has less than four digits, provided with sharp, 



conical claws, and very often there are five digits so provided. 



(7) Progression is digitigrade or plantigrade. 



(8) No digit is opposable to the others. 



(9) There are always well developed canines. 



(10) The incisors are small, and there are always six above and 

 six below in each jaw except in the marine otter {Enliy- 

 dris),^ and in the fossil Eus^nilus, which have each but 

 four inferior incisors. 



* The African aquatic Insectivore, named Polomocjale. 



