OF TKE CLASS MAMMALIA. 27 



is founded the name Proboscidia given to the order. The feet 

 are pentadactyle, but are indicated only by divisions of the hoof; 

 the testes are abdominal; the placenta is annular*; the mammae 

 are pectoral. 



Both the present and preceding orders of Ungulata may be 

 called aberrant : the dentition of the Toxodon, and several parti- 

 culars of the organization of the Elephant, indicate an affinity to 

 the E-odentia ; the cranium of the Toxodon, Kke that of the Dino- 

 there, resembles that of the Sirenia in its remarkable modifications. 



The typical Ungulate quadrupeds are divided, according to the 

 odd or even number of the toes, into Perissodacttla and Aetio- 

 DACTTLAf. In the perissodactyle or odd-toed Ungulata— < odd-toed 

 at least in regard to the hind-foot, — the dorso-lumbar vertebrae 

 differ in number in different species, but are never fewer than 

 twenty-two ; the femur has a third trochanter ; and the medullary 

 artery does not penetrate the fore-part of its shaft. The fore-part 

 of the astragalus is divided into two very unequal facets. The 

 OS magnum and the digitus medius which it supports are large, in 

 some disproportionately so, and the digit is symmetrical: the 

 same applies to the ectocuneiform and the digit which it supports 

 in the hind-foot. If the species be horned, the horn is single ; or, 

 if there be two, they are placed on the median line of the head, one 

 behind the other, each being thus an odd horn. The nasals expand 

 posteriorly. There is a well-developed post-tympanic process which 

 is separated by the true mastoid from the paroccipital in the Horse, 

 but unites with the lower part of the paroccipital in the Tapir, and 

 seems to take the place of the mastoid in the E-hinoceros and Hyrax. 

 The hinder half, or a larger proportion of the palatines enters into 

 the formation of the posterior nares, the oblique aperture of which 

 commences in advance either of the last molar, or, as in most, of the 

 penultimate one. The pterygoid process has a broad and thick base, 

 and is- perforated lengthwise by the ectocarotid. The crown of 

 from one to three of the hinder premolars is as complex as those of 

 the molars J : that of the last lower milk-molar is commonly bi- 

 lobed. To these osteological and dental characters may be added 

 some important modifications of internal structure, as, e.g. the 

 simple form of the stomach and the capacious and sacculated 



* Besides the annular placenta there is a subcircular villous patch at each 

 pole of the chorionic bag, by which it derived additional attachment to the 

 uterus, in the Elephant. 



f From 7repi(T(To^afcrvXos, qui digitos habet impares numero ; and apnos, 

 par, ^d/crvXos, digitus. 



X The extinct Lophiodonts form the sole known exception to this rule. 



