38 INSECTIVORA order i 



Subclass B. PLACENTALIA. 



Order I. INSECTIVORA.^ 



Generally small, pentadactyl plantigrades with daws. I often enlarged in part, 

 in other cases partly reduced. C differing hut slightly from I and P ; often large 

 and two rooted or rudimentary. P acuminate, the hindermost frequently secodont. 

 M lophodont or bunodont, the lower ones usually with five sharp tubercles, the upper 

 tri- or quadritubercular ; milk dentition usually shed early and seldom functional. 

 Brain small with smooth hemispheres. Clavicle almost always developed. 



The typical insectivores are small terrestrial animals, frequently sub- 

 terranean, burrowing and nocturnal in their habits, more rarely arboreal 

 or swimming, and subsisting on insects and worms. They form the most 

 primitive order among Placentalia, and are distantly related to the polyproto- 

 dont marsupials, at least to the Pantotheriidae. At present sevei'al absolutely 

 extinct forms are classed as insectivores, which frequently attain considerable 

 size, and which formerly were attributed to the primates, or were placed 

 in an order by themselves. 



At present, the insectivores inhabit only the Old World and North America, 

 not being found in South America or Australia. The fossil forms have 

 practically the same distribution, one genus only being confined to South 

 America. They begin with quite a number of extinct types in the Eocene 

 and Oligocene of North America, but play a very insignificant part in the 

 later Tertiary of that region, whereas in Europe they are not uncommon, 

 in spite of their small size, from the Oligocene to the Upper Miocene. 



The skull is distinguished by its low, flat outline, by the broad occiput, 

 by the usually well-developed facial bones, by the orbits generally opening 

 posteriorly, by the incomplete ossification of the auditory capsule, by the 

 ring-like tympanum and by the small brain-cavity. The cerebral hemi- 

 spheres are smooth; the zygomatic arch is frequently reduced. The lumbar 

 region often has intercentra. The humerus has as a rule an entepicondylar 

 foramen. Ulna and radius remain separated, whereas tibia and fibula are 

 frequently fused distally. The femur has sometimes a third trochanter. 

 The plantigrade hand almost always has five, veiy seldom four fingers. 

 The hallux disappears at times. Among the burrowing forms the bones 

 of the fore-limb are ver}' highly specialised. 



The jaAv contains all of the several varieties of teeth, but the C and 



front P are often hard to distinguish. The normal dentition „ ', ' .' ' is 



0.1,4.0. 



often reduced. The / are sometimes very long, almost rodent-like and having 



secondary tubercles. C not infrequently has two roots. The number of 31 



is never more than three. The last P frequently becomes molariform. M 



^ Dobson, G. E., Monograph of the Insectivora, systematical and anatomical. London, 

 1882-90. — Gaillard, C. , Manimiteres miocenes. Arch. Mus. Hist. Nat. Lyon, vol. vii., 1899. — 

 Gregory, W. K., The Orders of Mammals. Bull. Amer. Mus. Nat. Hist., vol. xxvii. , 1910. — 

 Leche, W., Zur Eutwicklimgsgeschichte des Zahnsystems der Saugetiere. Bibliotheca Zoologica, 

 Bd. XV. 1902; Bd. xx., 1907. — Matthew, \V. D., The Carnivora and Insectivora of the Bridger 

 Basin, Middle Eocene. Mem. Amer. Miis. Nat. Hist., 1909. — A Zalambdodout Insectivore from 

 the Basal Eocene. Bull. Amer. Mus. Nat. Hist., 1913. — Oshorn, H. F., American Eocene 

 Primates and the Mixodectidae. Bull. Amer. Mus. Nat. Hist., 1902. — Schlosser, M., Beitr. 

 Paliiontol. Osterr.-Ung.. Bd. vi., 1887. 



