102 INTRODUCTION TO CLASSIFICATION. 



In the following orders the placenta is NOX-DECIDUATE 



1. UNGULATA. There are two sets of enamelled teeth. The 

 molars have broad crowns with tuberculated or ridged surfaces. 



There are never more than four full-sized toes on each limb, 

 and the terminal digits are cased in thick hoof-like nails. 



The members of this group are ungnligrade or digitigrade, 

 never plantigrade. Clavicles are never developed. The teats 

 are few and inguinal, or numerous and abdominal, in position. 

 The placenta is diffuse or cotyledonary. 



The Ungulata are divisible into two sub-orders, which pass 

 into one another : (a), the Perissodaetyla (Horses, Ehinoceroses, 

 Tapirs, Palxoiheria, Macraucheniee), with the third digit of each 

 foot symmetrical in itself; the toes of the hind foot odd in 

 number ; a third trochanter on the femur ; the stomach simple, 

 and the csecum very large; the horns, if present, median, 

 and not supported by a bony core: (&). the Ariiodactyla 

 (Hippopotamuses, Pigs, Anoplotheria, Ruminants), with the 

 third digit of each foot paired with the fourth, and the func- 

 tional toes of the hind foot even in number; no third tro- 

 chanter; the stomach more or less complex, and the caecum 

 not so large. The horns, if present, paired, and supported by 

 a bony core. 



The Ungulata are closely allied with the Hyracoidea among 

 the Mammals with zonary placentation. 



2. The CETACEA. The body has a fish-like form, with a 

 horizontal expansion of integument as a caudal fin, and some- 

 times a vertical expansion, as a dorsal fin. The hairs are very 

 scanty. 



The anterior limbs alone are developed, and are fin-like and 

 devoid of nails. The nasal aperture, or apertures, are placed at 

 the top of the head. There is no third eyelid, and the teats are 

 two, and inguinal. 



In the skeleton the cervical region is short, and the lumbar, 

 long ; there is no sacrum, and no odontoid process in the 

 second cervical vertebra. The skull has a very broad brain 

 case, and the premaxillae, which are small in proportion to the 

 maxillfie, are prolonged far in advance of the nasal aperture. 

 The frontals have great supraorbital processes, and the maxillae 



