. Une introduction à l'étude des mammifères vivant et disparu. Les mammifères. Caractères généraux 129 fixé pour un temps considérable, nourri par le lait injecté dans la bouche par la compression du muscle pour la glande mammaire. Ils sont donc le plus souvent- mam de maliens l'ensemble de la classe. Les mamelons sont presque toujours caché dans un pli de la peau abdominale ou " pouch" (marsupium) qui sert à soutenir et protéger les jeunes au début de leur condition sans défense. Entrer plus pleinement dans les caractères de la sous-classe, qui sont également ceux de l'ordre Marsupialia, il

• Contributeur: The Book Worm / Alamy Banque D'Images
• ID de l’image: RE0A72
• Taille du fichier: 7,1 MB (142,7 KB Téléchargement compressé)
• Autorisations: Modèle - non | Propriété - non
• Dimensions: 2371 x 1054 px | 40,1 x 17,8 cm | 15,8 x 7 inches | 150dpi

Informations supplémentaires

Cette image appartient au domaine public, ce qui signifie que le droit d’auteur a expiré ou que le titulaire du droit d’auteur a renoncé à ses droits. Les frais facturés par Alamy couvrent l’accès à la copie haute résolution de l’image.

Cette image peut avoir des imperfections car il s’agit d’une image historique ou de reportage.

. An introduction to the study of mammals living and extinct. Mammals. GENERAL CHARACTERS 129 attached for a considerable time, nourished by the milk injected into the mouth by compression of the muscle covering the mammary gland. They are therefore the most typically mam- malian of the whole class. The nipples are nearly always concealed in a fold of the abdominal integument or " pouch" (marsupium) which serves to support and protect the young in their early helpless condition. Entering more fully into the characters of the subclass, which are also those of the order Marsupialia, it may be observed that the brain is generally small in proportion to the size of the animal, and the surface-folding of the cerebral hemispheres, though well marked in the larger species, is never very complex in character, and is absent in the medium-sized and smaller species. The arrangement of the folding of the inner wall of the cerebrum differs essentially from that of all known Eutheria, the hippocampal fissure being continued forward above the corpus callosum, which is of very small size. The anterior commissure is, on the other hand, greatly developed. The teeth are always divisible, according to their position and form, into incisors, canines, premolars, and molars; but they vary much in number and character in the different families. Except in the genus Phascolomys, the number of incisors in the upper and lower jaws is never equal. The true molars are very generally four in number on either side of each jaw. The chief peculiarity in the dentition lies, however, in the mode of succession. Thus there is no vertical displacement and succession of the teeth, except in the case of a single tooth on either side of each jaw, which is always the hindermost of the premolar series, and is preceded by a tooth having more or less of the characters of a true molar (see Fig. 34); this deciduous tooth being the only one comparable to the "milk-teeth "of the diphyodont Eu- t

Recherche dans la banque de photos par tags

• bookauthorly
• bookcentury1800
• bookdecade1890
• booksubjectmammals