Practical anatomy of the rabbit : an elementary laboratory text book in mammalian anatomy / by B.A. Bensley.
- Benjamin Arthur Bensley
- Date:
- 1918
Licence: In copyright
Credit: Practical anatomy of the rabbit : an elementary laboratory text book in mammalian anatomy / by B.A. Bensley. Source: Wellcome Collection.
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![DENTITION. As accessory structures the teeth of the rabbit present two mammalian features; they are heterodont, or differentiated according to particular regions; and the adult series, excepting those designated as molars, are permanent teeth, replacing deciduous, or milk teeth of the young animal. The condition is thus de- scribed as diphyodont in comparison with that in lower verte- brates. where there is usually a multiple tooth change, new teeth being developed as required (polyphyodont type). Moreover, in the rabbit, as in all mammalia, the number is restricted, so that, considering the differentiation of the teeth, it is possible to express their relations by a dental formula. In the mammalia generally the teeth are differentiated into incisors, canines, premolars and molars, and in placental mammals the full dental formula is indicated as i. {[, c. ], pm. {, m. jj. In the rabbit as in other rodents, however, the dentition is greatly modified by the elaboration of two pairs of incisors for gnawing and the corresponding obliteration of intermediate teeth, the place of the latter being occupied by an extensive gap, or diastema, in which no teeth occur. The dental formula of the rabbit is i. j, c. jj, pm. m. jj. It will also be observed in this animal that the absence of the intermediate teeth allows the lips to be approximated behind the incisors, and since in this region the lips are also provided with hairs on their internal surfaces, the oral cavity is separated almost completely from a small space enclosing the incisor teeth. This adaptation, however, is not so perfectly developed in the rabbit as in certain others of the rodent order. The human skull differs most markedly from that of the rabbit or other mammal in the enormous development of the cranial region, and in the anteroposterior compression of the face, with THE HUMAN *s associated, shortening of the jaw region, SKULL. reduction of the nasal cavities and rotation of the orbits to a forward position. A most instructive feature is the re-adjustment of the axis, coincident with the assump- tion of the erect position. In both quadrupedal and bipedal positions the lace naturally retains its forward direction. In most mammals, as in vertebrates generally, the axial line of the cranium, known as the basicranial axis, and that of the face, the basifacial axis, tend to be continuous or at least parallel; while in man,](https://iiif.wellcomecollection.org/image/b29820753_0063.jp2/full/800%2C/0/default.jpg)
