89 COMPARATIVE ANATOMY. 



their aquatic habits, and their tail is horizontally flattened. 



The Cats, or Felidm, are as I have already noticed, among 

 the most bloodthirsty of the carnivors. 



Their jaws are short, and powerful from the increased lever- 

 age, the ascending ramus of the lower jaw being higher in 

 proportion than in the dogs. 



Their dental formula is :- 



3—3 I— I 4—+ 2—2 



I c PM M 34 



3—3 I— I 2—2 I— I 



If you pass your finger into this large foramen, or hole 

 through which the spinal cord passes up to the brain, you 

 will feel a projecting bony ridge. 



This is an ossified tentorium., or bony substitute for the mem- 

 brane that in all mammalia separates the cerebellum, or back 

 part of the brain, from the cerebral hemispheres or fore-part of 

 the brain, and is found in the carnivorous animals that spring 

 on their prey, to protect the brain from concussion. 



The same phenomenon is also to be observed in the long- 

 necked ungulata, the weight of whose head necessitates a 

 similar provision. 



You all are familiar with the arrangement, common to all 

 the cats, whereby they are able to withdraw their claws, thus 

 keeping them always sharp and making their tread noiseless 

 when creeping stealthily towards their prey. 



I would also wish to call your attention to this large bladder- 

 like protuberance called the tympanic bone, or ear bone, which 

 is very large, almost absolutely as large as that in the skull of 

 this dog although the size of the skull is so much smaller. 



This marks its nocturnal habits. And here I would mention 

 the common saying that "cats can see in the dark; " this is 

 untrue ; their eyes are adapted for seeing in twilight and dusk 

 better than other animals that prey by day, from their 

 power of dilating the pupils of their eyes, so as to have the 

 fullest use of any light there may be ; but as to seeing when 

 there is no light, they can no more do so than we can. Much 

 of that acuteness of the cat, which is commonly attributed to 

 its powers of vision, is due to the greater power of hearing 

 with which it is endued. 



I can show you the same thing in this skull of an owl whose 

 habits are nocturnal ; and in this skull of a mole, whose vision 



