. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. MONOTREMATA. 371 illary bone (Jig. 169, m) extends backwards as far as tlie posterior boundary of the zygomatic or temporal fossa; the palatal process extends along the floor of the orbit in a similar form and to nearly the same extent. The orbit is marked off from the temporal fossa by merely a slight ridge extending down and across the suture joining the frontal and sphenoid bones. The skull of the Echidna differs from that of the edentulous Manis and Myrmecophaga in the completion of the zygomatic arches, in the unclo
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. MONOTREMATA. 371 illary bone (Jig. 169, m) extends backwards as far as tlie posterior boundary of the zygomatic or temporal fossa; the palatal process extends along the floor of the orbit in a similar form and to nearly the same extent. The orbit is marked off from the temporal fossa by merely a slight ridge extending down and across the suture joining the frontal and sphenoid bones. The skull of the Echidna differs from that of the edentulous Manis and Myrmecophaga in the completion of the zygomatic arches, in the unclosed state of the tympanic cavity, in the large size of the foramen incisivum, and the surrounding of the external nostrils by the intermaxillary bones alone: it differs also in the smaller relative distance between the poste- rior palatal fissure and the superior maxillary bones, and in the apparent absence of the pala- tine bones, the presence and interposition of which between the pterygoid and maxillary palatal plates elongates the palate in the pla- cental Anteaters at the part where it is rela- tively shorter in the Echidna. In the modi- fication of the pterygoid plates of the sphenoid to complete the posterior nasal canal, the Echidna manifests an interesting resemblance with the great Anteater; but it differs from this, as from every other mammiferous species, in the palatal plates contributed by the petrous bones to the broad posterior part of the roof of the mouth which supports the horny palatal teeth. Cuvier describes the posterior palatal fissure as extending between the palatine bones, and therefore regards the plates, which are here affirmed to be developed from the petrous bone, as being the pterygoid processes of the sphenoid; and, according to this view, he truly observes that their horizontal position is very remark- able;* but he might have added, that their share in the formation of the tympanic cavity was not less so. The same determination of the bones co
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