28 



ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 



position of the supernumerary incisors, and in the number, and direction of the 

 curvature, of the molars. If, moreover, the lower jaw, next to be described, be- 

 long, as I believe, to the Toxodon, the dental character of the genus will be 



incisors f ; pro laniariis diastema; molar es %\ . 



The Toxodon again deviates from the true Rodentia, and resembles the Wom- 

 bat, and the Pachyderms, in the transverse direction of the articular cavity of the 



lower jaw. 



It deviates from the Rodentia, and resembles the Pachydermata in the rela- 

 tive position of the glenoid cavities and zygomatic arches, and in many minor de- 

 tails already alluded to. 



In the aspect of the plane of the occipital foramen, and occipital region of the 

 skull ; in the form and position of the occipital condyles ; in the aspect of the plane 

 of the anterior bony aperture of the nostrils ; and in the thickness and texture of the 



_ 



osseous parietes of the skull, the Toxodon deviates both from the Rodentia and 

 existing Pachydermata, and manifests an affinity to the Dinotherium and Cetaceous 

 Order, especially the Herbivorous section. 



At present we possess no evidence to determine whether the extremities of 

 the Toxodon were organized on the ungulate or unguiculate type, nor can we be 

 positive, from the characters which the skull affords, that the genus may not be 

 referrible to the Mutica of Linnaeus;* although the development of the nasal cavity 

 and the presence of large frontal sinuses render it extremely improbable that the 

 habits of this species were so strictly aquatic, as the total absence of hinder ex- 

 tremities would occasion. 



Where the dentition of a mammiferous animal is strictly carnivorous, this 

 structure is obviously incompatible with a foot incased in a hoof : — but where 

 the teeth are adapted for triturating vegetable substances the case is different. 

 If animals so characterized are of small size and seek their food in trees, or if they 

 burrow for roots or for shelter, the vegetable type of dentition must co-exist with un- 

 guiculate extremities, as in the Edentata and Rodentia generally : but the largest 

 genus (Hydrochserus) of the Rodent Order, whose affinity to the Pachydermata is 

 manifested in its heavy shapeless trunk, thinly scattered bristly hair, and many 

 other particulars, has each of its toes inclosed in a miniature hoof. 



The affinity above alluded to, is too obvious to have escaped popular notice, 

 and the Capybara, from its aquatic habits, has obtained the name of Water-hog. 

 It is highly interesting to find that the continent to which this existing aberrant 



* The German Translator (See Frorieps Notizen., 1837, p. 119) of the abstract of my description of the 

 Toxodon, published in the Proceedings of the Geological Society, asks, what is the Mutica (misprinted Muticata), 

 of Linnaeus ? The term is quoted from the Systema Naturae, Ed. xii. p. 24. Linnaeus first divides Mammalia 

 into three groups, according to modifications of the locomotive organs, viz. Unguiculata, Ungulata, Mutica, and 

 subdivides these, according to modifications of the dentary organs, into the orders, Bruat, Glires, Primates, &c. 



