DENTITION. 51 



Stannius. in 1842, further contributed to the subject by 

 adding observations respecting variation in the number of 

 the teeth resulting from age, describing in detail the incisive 

 dentition of a series of four skulls of different ages. In two 

 young skulls, the outer temi^orary incisor of the upper jaw on 

 either side remained; the alveoli of the second pair were still 

 distinct, while the alveoli of the middle pair were nearly oblit- 

 erated. In another, the alveoli of the inner pair of incisors were 

 wholly obliterated ; those of the second pair were barely recog- 

 nizable, while those of the outer pair were distinct, the teeth 

 having faUen later. He was also able to recognize the alveoli 

 of six incisors in the lower jaws of the skulls just mentioned, 

 and states that he thought Eapp's view of the homology of the 

 first lower back-tooth (considered as a canine) was probably 

 correct. He further takes exceptions to the value of the char- 

 acters assumed by Fremery as the basis of several species of 

 Walruses.* He adds, in respect to the tusks, that in old 

 age they become wholly solid to the base. In regard to the 

 upper molars, he notes the i^resence of five in several instances, 

 and fmds that, as a rale, the fourth disappears before the fifth, 

 or, at least, that its alveolus becomes sooner obliterated. He 

 also confirms the statement previously made by Wiegmann, 

 that the alveoli become fiUed by depositions of bony matter in 

 concentric layers at the bottom and on the sides. 



*These alleged specific characters lie notices in detail, and considers them 

 as dependent upon age. He says: "Das Missliche dieser Cliaraktere erliellt 

 sclion aus dem Umstande, dass dieselben nur fiir vollig ausgewachsene Thiere, 

 nicht aber fur junge anwendbar sind, denn das stiirkste Wacbsthuni der 

 Eckziihne fiillt erst offenbar iu eine spiitere Lebensperiode in -welcher 

 namentlicli die beiden innersten Scbneidezaline und die beiden letzten Back- 

 ziihne jeder Seite der oberen Kinnlade schon gescliwunden sind. Hierzu 

 kommt noch der Umstand, dass aucb die Eckzaline bei sebr alteu Thieren 

 an der Spitze bedeutend abgeuutzt sind, demnacli in spateren Lebenssta- 

 dien an Lange wabrscbeinlicli wieder abnebmen. Endlich scbeint es ja 

 selbst, alsob die Lange dieser Zabne je nacb den Geschleclitem verscbieden 

 ware. 



"Eben so weuig Gewicbt mocbte ich auf die Furcbungen dieser Zabne 

 legen. Ikrer Zabl, wie ibrer Starke nacb sind sie bei verscliiedenen iibri- 

 gens nicbt von einander abweichenden Individuen versfbieden, wie icb 

 micb durcb Vergleicbung einer grossen Anzabl von Walrossziibnen iiber- 

 zeugt babe; ja diese Furcben sind bisweilen an beiden, bisweilen nur an 

 Einem dieser Ziibnc spurlos verscliwunden." 



Respecting Trichechus cookl, be adds: ''Aucb an einem Scbiidelfi-agmente 

 des Kieler Museums finde icb etwas convergirende Eckzabne, mocbte aber 

 zweifeln, ob dieser Umstaud eine Artunterscbeidung recbtfertigt." Muller's 

 ArcMv fiir Anatomie, etc., 1842, pp. 398, 399. 



