. Cassell's natural history. Animals; Animal behavior. IF THI-: UdDKS'l of this structiii-e of thiis strongly of the characters of the mohu's of the gigantic Proboscidea, in which, moreover, the incisors also ai-e represented by the permanently-gi-owing tusks. The articulation of the lower jaw with the skull is peculiar, and in special relation to the armature of teeth which we have described. Instead of articulating freely, as in man and many herbivorous mammals, by which provision is made for a sort of rotatory action of the molars, or by a regular trans- verse liinge-joint, as in the Caruiv
. Cassell's natural history. Animals; Animal behavior. IF THI-: UdDKS'l of this structiii-e of thiis strongly of the characters of the mohu's of the gigantic Proboscidea, in which, moreover, the incisors also ai-e represented by the permanently-gi-owing tusks. The articulation of the lower jaw with the skull is peculiar, and in special relation to the armature of teeth which we have described. Instead of articulating freely, as in man and many herbivorous mammals, by which provision is made for a sort of rotatory action of the molars, or by a regular trans- verse liinge-joint, as in the Caruivora, the articulating surfaces are elongated in a dii-ection parallel to the middle line of the skull, an ar- rangement which, like that occurring in Carnivora, has the efiect of preventing much lateral movement of the jaw; but, at the same time, the pits with which the jaw aiticulates are open in front, so that the jaw is allowed a certain amount of play, backwards and forwards. This motion greatly increases the gnawing power of the large incisor teeth. The head in the Rodents is gene- rally of small or moderate size in pro- portion to the body, and the skuil is usually rather elongated, and flattens on the upper sui-face. The tympanic bnlliB are generally of considerable size ; the zygomatic arch is in nearly all cases well developed; but the orbits of the ^kllet n of the Kiuir eyes are never closed behiud, and only in certain families is there even a small ])rocess of the zygomatic arch behind the orbits, as an indication of possible closure. Of the vertebral column we need only say that the lumbar vertebr:e are remarkable for possessing large transverse processes directed forwards, and that the tail varies * The genus Hdiophohius among the Jlole Eats is describefl as having six molars on each side in both jaws ; but the number in this genus appears to be variable, the sixth molar being often Please note that these images are extracted from scanned page images
Size: 1756px × 1422px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjecta, booksubjectanimals
