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rupted between the inflected border (d) and the hinder inflection or angle a ; the slight 

 concavity between d' and a being less apparent in the adult jaw. The ridges (fig. 1, h, q) 

 bounding the ectocrotaphyte depression (f) are naturally feebler, less pronounced, in this 

 young jaw; the base of the anterior one (q) rises from the transverse parallel of the 

 hind lobe of the penultimate molar {m 2). The postinternal angle of the formative 

 alveolus of the last molar appears to represent the postalveolar process of the mature 

 mandible. 



The oblique channel (answering to u in figures of the adult jaw) between the coronoid 

 and postmolar processes here runs from that lodging the fore lobe of the penultimate 

 molar to near the middle of the outer part of the interspace between the lobes of the 

 antepenultimate molar [m 1) ; it thus preserves its general relative position to the last 

 grinder " in place" and use, and doubtless was still more advanced when m 1 was " en 

 germe." 



Such changes in the relative position of parts, and differences of general shape, of the 

 mandible in the adult and young Notothere are dependent on, or concomitant with, 

 the growth called for to sustain in action the full complement of teeth in the adult. 

 No inference of specific difference can be deduced from the relative position of the hind 

 part of the " symphysis mandibular" (?) in this young jaw to the front lobe of the second 

 molar (d 4) ; because the socket of that tooth would move forward in the course of growth, 

 whilst the symphysis extended its grasp of the fore parts of the two rami prior to the 

 ultimate obliteration of the syndesmotic joint in the adult. At the present immature 

 stage this articulation remains. The surface (fig. 4, s*) is vertical, flat, with roughish 

 rugae, mostly directed from above downward and forward, gaining in prominence, through 

 deepening of the intervals, along the lower third. It seems as if confluence had already 

 begun at a small part of the upper and posterior border of the articular surface, such 

 portion having been broken away from the left ramus and left adherent and seemingly 

 confluent with the right one. Behind the lower part of the posterior border of the 

 symphysis is the flattened, rough, slightly depressed surface (fig. 2, v) for muscular 

 insertion noted in the older specimens. 



The shallow indent or concavity dividing the inflected parts of the horizontal (d') and 

 ascending (a) rami has a more advanced position and a direction more approaching 

 the horizontal than in the mature jaw: in Plate XL. fig. 4, a-d! is shown to be below 

 the interval between the penultimate and last molars and parallel in extent with the 

 contiguous lobes of these teeth. The inward extension of the bone at a, fig. 4, represents 

 a resumption of the inflection of the lower margin of the jaw at its hinder part, from 

 which resumption the bone thins off to be continued backward into the thickened part (e), 

 which contributed to support the broken-off condyle. 



This character is retained, but is better marked, in the adult mandible of Notothei'ium 

 Victories from South Australia (Plate XLI.) ; but the incisor tooth in that species has a 

 smaller and more advanced socket than in the present immature jaw, which in this more 

 important character agrees with Nototherium Mitchelli. 



22* 



