. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. CRANIAL MORPHOLOGY OF THE DIGYNODONT GENUS LYSTROSAURUS 187 J AC- DUCT NO PAL PROC L AT PAL FOR LAB. FOS. Fig. 24. Lystrosaurus declivis. Nat. Mus. No. Skull in ventral view. in a complex suture, to a point just behind the descending palatal rim. Pos- teriorly the ridge is high and sharp, but flattens out anteriorly. On each side of the ridge is a narrow, deeply incised channel, opening out on to the palatal surface at the tip of the ridge. The lateral palatal ridges lie on the anterior descen
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. CRANIAL MORPHOLOGY OF THE DIGYNODONT GENUS LYSTROSAURUS 187 J AC- DUCT NO PAL PROC L AT PAL FOR LAB. FOS. Fig. 24. Lystrosaurus declivis. Nat. Mus. No. Skull in ventral view. in a complex suture, to a point just behind the descending palatal rim. Pos- teriorly the ridge is high and sharp, but flattens out anteriorly. On each side of the ridge is a narrow, deeply incised channel, opening out on to the palatal surface at the tip of the ridge. The lateral palatal ridges lie on the anterior descending rim of the palate, each arising laterally to the anterior tip of the median ridge and terminating as a ventral projection beyond the level of the rest of the premaxillary rim. Each ridge is cut down the middle by a single channel, similar to those along- side the median ridge. It seems probable that these grooves housed nutrient blood-vessels running between the bony ridges and a layer of horn. The pre- sence of horn on the ridges is further suggested by the porous, roughened surface of the bone. The extent of the horny beak on the palate will be more fully discussed in a later section. Posteriorly the premaxilla divides the nasal passages as a median septum, and terminates as a sharp blade enclosed by the diverging anterior wings of the vomer (Figs 2, 28, 35). Van Hoepen (1913) mentioned this suture in Lystrosaurus latirostris, and Barry (1967) found a similar interdigitating con- tact in Pristerodon. The increase in size of the premaxilla in Lystrosaurus as compared with other dicynodonts, is reflected in the great dorsoventral extent of this posterior sheet. The ventral half of the premaxilla-vomer suture is more complicated, there being a median septum of the vomer extending between two diverging internal premaxillary processes. Furthermore, a lateral fold of. Please note that these images are extracted from scanned page images that may have been digitally enhanced for
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
