Page:The American Cyclopædia (1879) Volume XI.djvu/90

82 MAMMALIA to the valne of the principal modifications ol the mammalian brain in regard to their asso- ciation with concurrent modifications in other systems of organs; it was not till 1857, how- ever, that he felt himself justified in proposing to the Linnsean society a fourfold division of this class, based upon the four leading modifi- cations of the cerebral structure. His first and lowest group or sub-class is called lyen- cetphala, signifying the loose or disconnected state of the cerebral hemispheres, which leave exposed the olfactory ganglia, the cerebellum, and more or less of the optic lobes, have the surface generally smooth, and the anfractu- osities, when present, few and simple ; in this division the absence of the corpus callosum commissure is associated with the marsupial mode of development and the non-develop- ment of the placenta ; it includes the mono- tremes and marsupials. The next stage in the development of the brain is where the corpus oallosum is present, but the hemispheres leave the olfactory lobes and cerebellum exposed, and are commonly smooth or with few and simple convolutions ; these are the listencepTia- &, or smooth-brained mammals, or rodents, insectivora, bats, and edentates, in many re- spects, in common with the preceding subdi- vision, resembling birds and reptiles. The tldrd modification is an increased relative size of the hemispheres, which extend over more or less of the cerebellum and olfactory lobes, and have their surface, except in a few of tho lower quadrumana, folded into more or less numerous gyri or convolutions ; hence this sub-class is called gyrencephala ; among these are not found marks of affinity with the ovi- para, but the highest mammalian perfection is attained, as shown by the size, strength, ac- tivity, sagacity, and docility of many of its members; this sub-class comprises the other orders of mammals, man only excepted. In man the hemispheres overlap the olfactory lobes and cerebellum, extending in advance of the former and further back than the latter ; in man only is there what is called a third or posterior lobe, and in him the superficial gray matter attains its highest development through the number and depth of its convolutions ; as representing a distinct sub-class of mammalia, and ruling naturally over all the other mem- bers of the class, he proposes for man the name of archencephala, signifying that he is master of the earth and of the lower creation. For details on the characters of the secondary groups and their distribution in time and space, the reader is referred to the original paper in the "Proceedings of the Lmnsean Society" of London, vol. ii., pp. 1-37, 1857. His tabular arrangement is as follows : f ABOHIHOKPHALA BIMAKA.. MAMMALIA. f Unguiculata . OTBIBOXPHALA. Ungulate. LnUKOXPHALA . LTKfOIPBALA. fQUADBTJMANA.., [CABNIVOBA ABTIODAOTTLA PEBISSODAOTYLA... PROBOSOIDIA ....... TOXODONTIA ....... f SlBENIA [CETAOBA.. BBDTA CHJBIBOPTEBA. . INBEOTIVOBA. EODENTIA. I MONOTBEMATA . . . The later classification of Huxley does not dif- fer materially in its orders from that of Owen "g the many recent American labor- re in the department of mammalian classifica- tion may be mentioned Prof. Theodore Gill of Washington, D. C., whose articles on this j'ilj.-rt too long to be condensed here, will be found in the " Proceedings of the American Family or genu. Example. Homo Man. Catarhina Ape. Platyrhina Marmoset Strepirhina Lemur. Digitigrada Dog. Plantigrada Bear. Pinnigrada Seal. Omnivora Hog. Ruminantia Sheep. J Solidungula Horse. | Multungula Tapir. j Elepha* Elephant. DinotJierium Extinct. Toxodon " Nesodon Manatus Sea cow. Halicore Dugong DelphinidcB Porpoise. Balasnidce Whale. BradypodidcB Sloth. Dnsypodidce Armadillo. Edentula Ant-eater. Frugivora Roussette. Insect irora Bat Talpidce Mole. Erinaceidce Hedgehog. SoricidcR Shrew. Non-claviculata. . . . Hare. Clamculata Rat. Rhizophaga Wombat. Poephaga Kangaroo. Carpophaga Phalanger. Entomophaga Opossum. Echidna Echidna. Ornithorhynchus.. . . Duck-bill. Association for the Advancement of Science " for 1870 and 1871. The fossil mammals must be considered before the student can form an idea of the affinities of the class; these and the orders of existing mammalia will be treated under their respective titles. The mammalian class has existed certainly from the lower oolitic penod, and probably from the triassic ; during