that it is on the whole advisable to regard them as representing a distinct suborder of Carnivora. In the strong development of the canines (Fig. 278) they are distinguished from the modern Insectivora; and they also differ from the latter and resemble the true Carnivores in the form of the incisors, the second one in the lower jaw (when three are present) being thrust up above the level of the other two in the manner obtaining in most of the modern Carnivora. Some of the most generalised forms included in the present group approximate so closely to the Condylarthrous Ungulates as to indicate that both groups have probably had a common origin.

The Creodonta as a whole are characterised by the small size of the brain, the absence of a single differentiated carnassial tooth, and the triangular form or secant character of their upper molars. In the carpus the scaphoid and lunar were usually distinct; the femur has a third trochanter; the upper or tibial surface of the astragalus usually wants the groove found in modern Carnivores : and the feet were plantigrade. The curious resemblance of the molars of many of these forms to those of the Marsupials may indicate a genetic relationship between the two groups; but, on the other hand, the presence of a full set of milk-teeth and the absence of palatal vacuities, or of an inflection of the angle of the mandible, sharply distinguishes them from that order. Space permits of a notice only of the more interesting forms.

Hyaenodontidae.-This family is taken to include some of the more specialised types, such as the European and American Hyænodon and Ochyana and the European Pterodon. In Hyonodon (Fig. 278) the dental formula is i, c, p, m; the fourth premolar above and the first true molar below being formed upon the "carnassial" plan, but the teeth behind these, instead of being tuberculated as in all existing Carnivora, repeat the characters of the carnassial, and also increase in size, especially in the lower jaw, from before backwards. The last lower molar differs from the two preceding teeth, and is very like the carnassial of Felis. The scaphoid and lunar of the carpus were fused together. Some species, as H. leptorhynchus, were as large as a Wolf, while others did not exceed a Fox in size. Pterodon is readily distinguished by having m, by the larger size of the inner tubercles of the upper molars, and the similarity in the form of the three lower molars. In some species there were only two upper incisors, and the first lower premolar may be wanting. Oxhyena is a specialised form with i3, ci, p, m, and a very long mandibular symphysis.

Proviverrida.—The European and American genus Proviverra (Cynohyanodon or Stypolophus) may be regarded as representing a second family. The dental formula in this genus is the typical i 3. ci, pt, m3, the upper molars have a large inner tubercle, while the lower molars are differentiated into a blade and talon, the

blade having a large inner cusp. The upper teeth closely resemble the molars of Dasyurus, while the lower molars are like the lower carnassial of Cynodictis and Viverra; and thus indicate how the Creodonts may have passed into the true Carnivores through the extinct Miacidæ.

?

Arctocyonidae and Mesonychida.-The first of these families is represented by Arctocyon primavus, one of the oldest known Tertiary mammals, from the lowest Eocene beds of La Fère, department of Aisne, France, and also by other species from corresponding beds at Rheims. The dental formula is i, c, P, m3. The upper molars (Fig. 279) are tritubercular, with an incipient posterointernal column (hypocone); the lower are quadritubercular; and the premolars simple. The typical species was of large size, but the two of which the teeth are figured were considerably

a

m

paracone; me, metacone; hy, hypocone; ml, meta

conule; pl, paraconule. (From Osborn.)

FIG. 279.-The three right upper molars of Arctosmaller. In the American cyon dueli (a), and the second of A. gervaisi (b); from Mesonyx the dental formula the Lowest Eocene of Rheims. pr, protocone; pa, was the typical one, the jaws were comparatively short, the mandibular symphysis was elongated, the cheek-teeth were of simple structure, and resembled the premolars of many of the true Carnivora, and the astragalus had a grooved tibial surface and distinct distal facets for the cuboid and navicular, resembling in the latter respect the corresponding bone of a Perissodactyle Ungulate. The terminal phalanges had deeply fissured extremities, and are said to be more like those of Rodents than true Carnivores. Mesonyx ossifragus was larger than a Grizzly Bear. Amblyctonus, of the same deposits, differs by the smooth tibial face of the astragalus and the development of an anterior cusp to the lower molars.

CHAPTER XII

THE ORDER INSECTIVORA

THE Insectivora comprise a number of comparatively small mammals, generally of terrestrial, although rarely of arboreal or aquatic habits, and presenting the following common features. They are unguiculate, and have plantigrade or subplantigrade, and generally pentadactylate feet, in which the pollex and hallux are not opposable to the other digits. They are diphyodont and heterodont, and the teeth are rooted. The molars are studded with sharp cusps, the crowns of the upper molars being either quadrangular or triangular; there are never less than two incisors in either side of the mandible; and in many cases the incisors, canines, and anterior premolars are not clearly differentiated from one another (Fig. 280);

FIG. 280.-Right lateral aspect of the anterior portion of the cranium of Erinaceus collaris. Enlarged. (From Dobson, Proc. Zool. Soc. 1881, p. 403.)

the canines being usually weak. Clavicles are present, except in Potamogale. The body is clothed with fur or protected by an armature of spines; the testes are inguinal or placed near the kidneys,

and are not received into a scrotum; the penis is pendent or suspended from the wall of the abdomen; the uterus is two-horned and with or without a distinct corpus uteri; the placenta is discoidal and deciduate; and the smooth cerebral hemispheres do not extend backwards over the cerebellum (Fig. 281). The projection of the muzzle far beyond the extremity of the lower jaw is a very general feature. The humerus generally has an entepicondylar

foramen.

Certain forms, such as Talpa and Galeopithecus, are unique among mammals in having ossified intercentra in the dorso-lumbar region of the vertebral column.

Representatives of this order are found throughout the temperate and tropical parts of both hemispheres (except South America and Australia), and exhibit much variety both in organisation and in habits. With the exception of the Tupaiida, all are nocturnal; the greater number are cursorial, but some (Talpa, Chrysochloris, Oryzorictes) are fossorial; some (Potamogale, Nectogale, Myogale) are natatorial, and a few (Tupaide) arboreal; while the species of the aberrant genus Galeopithecus glide through the air like the Flying Squirrels. To the great majority the term insectivorous is strictly applicable, Galeopithecus alone being phytophagous; while Potamogale is said to feed on fish, and the different species of Moles live chiefly on worms. The general organisation of the Insectivora indicates a very low type, and were it not for the specialised character of their placentation and the tendency to lose the differentiated characters of the anterior teeth they might be regarded as closely allied to the ancestral type of many of the heterodont mammals. The strongly marked distinction of the canines from the incisors and anterior premolars in the Mesozoic and most of the Tertiary mammals (excepting some of the Ungulates) points, however, very decidedly to the conclusion that the want of definition between these teeth in many of the modern Insectivora is an acquired feature. Fossil forms apparently indicate a relationship on the one hand with the Creodont Carnivora, and on the other with the Lemuroid Primates; indeed it is in some instances impossible to say whether extinct genera are really Insectivores or Lemuroids.

FIG. 281.-Upper surface of the brain of Tupaia ferruginea. (From

Garrod, Proc. Zool. Soc. 1879, p. 304.)

In most Insectivora the cranial cavity is of small relative size, and in none is the brain-case elevated to any considerable extent above the facial line. The facial part of the skull is generally much produced, and the premaxillary and nasal bones are well developed. The zygomatic arch is usually slender or deficient, the latter being the case in most of the species; and postorbital processes of the frontals are found only in the Galeopithecida, Tupaiidæ, and Macroscelidida. The number of dorsal vertebræ varies from 13 in Talpa to 19 in Centetes; that of the lumbar from 3 in Chryso

chloris to 6 in Talpa and Sorex; and of the caudal from the rudimentary series of 8 in Centetes to the 40 or more of Microgale. Not less variable are the characters of the vertebræ themselves; the spinous processes often being very long in one and short in another species of the same genus. In the Soricida and Myogale the neural arches of the cervical vertebræ are very slender. In the Soricide and Gymnura the four anterior vertebræ develop large single hypapophyses. In Galeopithecus the centrum of each vertebra supports posteriorly a pair of intercentral ossifications; while in Erinaceus, Myogale, and Talpa small oval ossicles are found on the inferior surfaces of the lumbar interspaces. In Erinaceus, owing to the thickness of the neural cord in the cervical region and its abrupt termination, the diameter of the neural canal in the cervical and first two dorsal vertebræ greatly exceeds that of any of the succeeding vertebræ. The sternum is variable, but generally narrow, bilobate in front, and divided into segments. The pectoral girdle presents some remarkable adaptive modifications, most fully expressed in Talpa, having relation to the use of the fore limbs in burrowing; but in the Golden Moles (Chrysochloris) the forearm and manus alone become specially modified for this purpose. In Galeopithecus and Macroscelides the bones of the forearm (radius and ulna) are distally united. The manus has generally five digits, but in Rhynchocyon and in one species of Oryzorictes the pollex is wanting, while in the true Moles it is extremely modified. The femur has, in most species, a prominent ridge below the greater trochanter representing a third trochanter. In Galeopithecus, Tupaia, Centetes, Hemicentetes, Ericulus, and Solenodon the tibia and fibula are distinct, but in all the other genera more or less united together. The pes usually possesses five digits (rarely four by reduction of the hallux); and in some forms, as in the leaping species (Macroscelides, Rhynchocyon), the tarsal bones are greatly elongated. The form of the pelvis, and especially of the symphysis pubis, varies within certain limits; and these differences have been proposed by Leche as a basis for the classification of the families. Thus in the Galeopithecida, Tupaiida, and Macroscelidida there is a long symphysis; in the Erinaceida, Centetida, and Potamogalide the symphysis is short; and in the Soricidæ, Talpida, and Chrysochloride there is none.

Space does not admit of attempting a sketch of the modifications of the muscular system, which will be found fully described in Dr. Dobson's Monograph, referred to in the bibliography. As to the nervous system, it has been already mentioned that the brain throughout the order presents a low type of organisation; in none of the members do the cerebral hemispheres present any trace of convolutions, nor do they extend backwards so as to cover the cerebellum, while the olfactory lobes are large and project in front,