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Show 112 ON QI,ASSIFIOATJON. I.n d e b te d t o D r. Sha rpey .jcl or· valuable information respectin• g th•e I t f Manis The surface of the chonon Is placenta struc ure o · . . . d h . d 1 . covere d WI' th fi ne I.e t I'C · ulati'ng ndges ' 1nterrupte ere an. t 1.e re b y ronn d b a ld sp Ots ' g·ivinba it an alveolar aspe•c t, Tso me·t lnng. hke the I· nsi' d e of the human gall-bladder, but finer.. he rnner sur- 11 . . 1 . face of the uterus exhibits fine low ridges or vr 1, not retiCu atmg quite so much. The chorio~ presents ~ Land, free ~rom villi, running longitudinally along rts concavity, and the~e IS ~ corresponding bald space on the surfac~ of the uterus. 'I.he ndges of the chorion start from the margins of the bald stnpe, and run round the ovum. The umbilical vesicle is fusiform. This is clearly a non-deciduate placenta, and the cotyledonary form of that of the Sloth leads me to entertain little doubt that it belongs to the same category. Admitting all these difficulties and gaps in our information, it still appears to me that the £ atures of the placenta afford ?Y !'ar the best characters which have yet been proposed for class1fymg the Monodelphous Mammalia, especially if the concomitant modifications of the other frotal appendages, such as the allantois 'and yelk-sac, be taken into account. And it n1ust be recollected that any difficulti s offered by the placental method attach with equal force to the y terns of clas ification based upon cerebral characters which have hitherto been propounded. If any objections, on the ground of g neral affinities, ar.e offer~d to the association of Elephas, Hyrax, Felis, and Cercopithecus m. the same primary mammalian clivi ion of d ciduate Monodelphia, they are not removed by constructing that pri1nary division upon other principles, and calling it Gyrencephala. 11:1 LECTURE VII. ON TI-IE VERTEBRATE SI\ULL. THE STRUCTURE OF THE HUMAN SKULL. 'fHE human skull is by no n1eans one of the simplest exainples of a vertebrate cranium which can be studied, nor is the coinprehension of its structure easy; but, as aU vertebrate anatomy has started frmn the investigation of hu1nan organization, and the terms osteologists use are derived from those which were originally applied to definite parts of the organism of man, a eareful investigation of the fundamental structure of man's skull, becomes an indispensable preliminary to the establishment of anything like a sound comparative nomenclature, or general theory, of the Vertebrate Skull. Viewed from without (Fig. 47), the human cranium exhibits a multiplicity of bones, united together, partly by sutures, partly by anchylosis, partly by 1noveable joints, and partly by ligaments; and the study of the boundaries and connections of these bones, apart from any reference to the plan discoverable in the whole construction, is the subject of the topographical anatomist, to whom one constantly observed fact of structure is as valuable as another. The morphologist, on the other hand, without casting the slightest slur upon the valuable labours of the topographer, endeavours to seek out those connections and arrangements of the bony elements of the complex whole which are fundamental, and underlie all the rest; and which are to the craniologist that which physical geography is to the student of geographical science. I |
