. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 222 ANNALS OF THE SOl'TH AFRICAN MfSEUM. Fig. 53. Comparison of the skull of Lystrosaurus with that of a Permian dicynodont. {a) Lystrosaurus declivis, Nat. Mus. No. ; {b) Dicynodon sp., No. 8784. septum. The deepest part of the skull is at the level of the canine tusks and the vomer-premaxilla suture. The very deep snout and enlarged premaxilla have necessitated a new orien- tation of the nasal passages (Fig. 54). In typical dicynodonts the palatal plate of the premaxilla is thin and hor
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 222 ANNALS OF THE SOl'TH AFRICAN MfSEUM. Fig. 53. Comparison of the skull of Lystrosaurus with that of a Permian dicynodont. {a) Lystrosaurus declivis, Nat. Mus. No. ; {b) Dicynodon sp., No. 8784. septum. The deepest part of the skull is at the level of the canine tusks and the vomer-premaxilla suture. The very deep snout and enlarged premaxilla have necessitated a new orien- tation of the nasal passages (Fig. 54). In typical dicynodonts the palatal plate of the premaxilla is thin and horizontally disposed, and the respiratory passages lie in an anteroposterior direction, with the choanae only slightly below the level of the nostril. In Lystrosaurus the premaxilla is enormously thickened below the nasal aperture, thus displacing the internal nares far ventrally. The direction of the respiratory passages thus became dorsoventral rather than antero- posterior. Furthermore, a choanal tube leading from the nasal capsule to the internal nares, such as was suggested for the Gorgonopsia by Kemp (igGga), would, in comparison with other dicynodonts, have been considerably elongated in Lystrosaurus. The remainder of the skull has not followed the deepening of the snout to the same extent, with the result that the palate of Lystrosaurus is divided into two planes which meet at an angle at the level of the caniniform processes. The. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original South African Museum. Cape Town : The Museum
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
