INVERTEBRATE ZOOLOGY. 55 



Order 3. Sirenia Aquatic forms with only the anterior 



limbs developed. Teeth often fail : mo- 

 lars, when present, resemble those of vin- 

 gulates. Sparseh' hairy. A single pair 

 of pectoral mammary glands. 

 ■^ Manatus. 



Order 4. Ungnlata Herbivorous mammals with flattened 



molars. Toes often reduced in number, 

 tipped with flattened hoofs. 



Sub-order 1. PeiHssndactyla ... .JJngnhites with an odd number of toes. 



five, three or one. the middle one being 

 the best developed. Prae-molars equal 

 the molars in size. Integment often verj- 

 thick, if Rhinocero.'i. Eqniis. 



Sub-order 2. Artiodactyla Ungulates with an even number of toes. 



of which two. (3 and 4) are the best de- 

 veloped, resulting typically in the cloven 

 hoof. The prae-molars, 3-4, are smaller 

 than the molars. Apart of them are 

 ruminants. -^ i?o.s. Hippopotamus. 



Orders. Proboscidia A group allied to the Ungulates. Imt 



with always five stout toes furnished 

 with hoofs, making a ponderous rounded 

 foot. The snout is enormously prolonged 

 forming a muscular proboscis tipped with 

 a sensitive finger-like process. One pair 

 of incisors, which develop into mam- 

 moth tusks. In recent forms it is those 

 of the upper jaw. (Lower incisors in 

 lHnof]i('i-iit)ii.) if Elephan. 



Order 6. Rodentia A group of small animals with teeth fit- 

 ted for gnawing. One pair of incisors 

 in each jaw develop into sharp ciitting 

 chisels. Canines fail. The molars are 

 fitted with transverse ridges for cutting. 

 if Mk.s. SeiKniK. 



