Page:Encyclopædia Britannica, Ninth Edition, v. 15.djvu/422

Rh 400 MAMMALIA [iXSECTIVORA. dorsal fin. It constitutes the genus Lcucorhamplius of Lilljeborg, and Dclpliinapterus of other authors ; this last name, however, was originally bestowed on the Ik-luga, and should be retained for it. Bibi iograp/iy of Cetacea. D. F. Eschricht, Untersuchimgen iiber die Nvrdischen Walllhiere, 1849, contains a copious bibliography of the group up to the (late of publication. Since that time numerous monographs on (-pedal families and genera have been published, and a large illustrated general work, Osteographie desCetace s, by P. J. Van Ueneden and P. Gervais, 1868-79. See also J. F. Brandt, &quot; Unter- suchungen iiber die Fossilt-n und Subfossilc n Cetaceen Europa s,&quot; in Mem. de I Acad. Imp. de &amp;lt;SY. PAtrtbourg, 7th ser. t. xx., 1873; and C. M. Scammon, Marine Mammals of the N. W. Coast of North America, 1874. ORDER INSECTIVORA. Terrestrial, rarely arboreal or natatorial, diphyodont, heterodont, placental mammals of small size, with planti grade or semiplantigrade, generally pentadactyle, unguicu- late feet ; with clavicles (except in Potamogale) ; with more than two incisors in the mandible, and with enamel- coated molars having tuberculated crowns and well-de veloped roots. 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 discoidal and deciduate ; and the smooth cerebral hemispheres do not extend backwards over the cerebellum. 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 organization and in habit. The greater number are cursorial, but some (Talpa, Cltrysochloris, Oryzorictes) are fossorial, some (Potamogale, Nectogale, Myogale) natatorial, and some (Tupaiidse) arboreal, while the species of one genus (Gfaleopitkecus) glide through the air like Flying Squirrels; to the great majority, however, the term insectivorous is applicable, the aberrant Galeopithecus being alone phyto phagous also, while Potamogale is said to feed on fish, and the different species of Moles live chiefly on worms. Notwithstanding the homogeneous nature of their food, much variety prevails in the form and number of their teeth, as will be seen when we come to consider the classification of the species. In many the division into incisors, canines, premolars, and molars may be readily traced, but in others, forming the great majority of the species, such as the Shrews, this is accomplished with difficulty. The dentition of the Insectivora may, however, be considered typical, since from it may be derived, by modification, that of any known species of diphyodont placental Mammalia. This typical dentition is especially noticeable in the genus Gymnura, where the dental formula is i, c T , pm , m ; total 44 teeth. So also, in their general organization, these animals appear to have departed so little from what must have been the original mammalian type that, were it not for the apparently advanced character of their placentation, they might easily be considered the scarcely modified descendants of the ancestors of all other orders of diphyodont placental mammals. Their study, therefore, affords the best intro duction to that of this division especially. In most Insectivora the cranial cavity is of small relative size, and in none is the brain case elevated to any con siderable extent above the face-line. The facial part of the skull is generally much produced, and the premaxillary and nasal bones well developed. The zygomatic arch is usually slender or deficient, the latter being the case in most of the species, and post-orbital processes of the frontals are found only in Gfaleopitkecidee, Tupaiidx, and Macroscelidx. The number of dorsal vertebrae varies from 13 in Tupaia to 19 in Centetes, of lumbar from 3 in Chrysochloris to 6 in Talpa and Sorex, and of caudal from the rudimentary vertebrae of Centetes to the 40 or more well-developed ones of Microgale. Not less variable are the characters of the vertebrae : the spinous processes may be very long in one species and short in another, though belonging to the same genus ; in the Soricidse, and in Myogale the neural arches of the cervical vertebrae are very slender ; in Soricidse, also and in Gymnura the four anterior vertebrae develop large single hypapophyses, and in Galeopithecus the body of each supports posteriorly a pair of hypapophysial tubercles. 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 cord in the cervical region and its abrupt termination, the diameter of the neural canal in the cervical and first two dorsal vertebrae greatly exceeds that of any of the succeeding vertebrae. The sternum is variable, but generally narrow, bilobate in front, and divided into segments. The shoulder-girdle presents remarkable adaptive modifications, most expressed in Talpa (see MOLE), having relation to the use of the fore limbs in burrowing ; in the Golden Moles (Chrysochloris), however (vide infra), the forearm and manus alone become specially modified. In Galeopithecus and Macroscelides the forearm bones are distally united; in all other known Insectivora the radius and ulna are distinct. The manus has generally five digits, but in Rhynchocyon and in one species of Oryzorides the pollex is wanting. In the true Moles (see MOLE) it is extremely modified. The femur has, in most species, a prominent ridge below the greater trochanter presenting the characters of a third trochanter. In Galeopithecvs, Tupaia, Centetes, Hemicentetes, Ericidus, and Solcnodon the tibia and fibula are distinct, in all other genera more or less united together. The pes consists usually of five digits (rarely four by reduction of the hallux), and in some, as in the leaping species (Macroscelides, Rhynchocyon}, the tarsal bones are greatly elongated. The form of the pelvis, and especially that of the symphysis pubis, varies within certain limits, which have been proposed by Leche as a basis for the classification of the families. Thus in Galeopithecidse, Tupaiidx, and Macroscelidse, there is a long symphysis, as in Rodents ; in Erinaceidse, Centetidse, and Potamogalidse, it is short; and in Soricidee, Talpidx, and Chrysocldoridx there is none. Space does not admit of even attempting a sketch of the interesting modifications of the muscular system, which will be found fully described in the present writer s Mono graph, referred to in the bibliography. As to the nervous system, it may be noticed that the brain throughout the species presents a low type of organization: in none do the cerebral hemispheres present any trace of convolutions, nor do they extend backwards so as to cover the cerebellum ; the olfactory lobes are large and project in front; and the corpus callosum is short and thin. In the Hedgehogs ( Erinaceus) the spinal column ends abruptly opposite the third or fourth dorsal vertebra in a slender filament; the dorsal and lumbar nerves, given off in front of this point, ai e carried backwards in two compressed bundles occupying the suddenly narrowed spinal canal as far as the sacrum. Owing to the similarity in the character of the food, the truly insectivorous species, forming more than nine-tenths of the order, present little variety in the structure of the digestive organs. Except in Galeopithecus (vide infra) the stomach is a simple, thin-walled sac ; in some, as in Centetes and allied genera, the pyloric and oesophageal openings are very close together ; the intestinal canal has much the same calibre throughout, and varies from three (in the Shrews) to twelve times (in the Hedgehogs) the length of the head and body. In the arboreal genera, Galeopithecus and Tupaia, and in the allied Macroscelidse, all of which probably feed on vegetable substances as well, most of the species possess a ceecum. The liver is deeply divided into