1892,] MILK-DENTITION OF PROCAVIA CAPENSIS. 41 



marked cervix, and a simple single fang, slightly constricted at its 

 base. The smaller posterior one (fig. 2, di^) is much simpler and 

 not so much calcified, and although it had no distinct fang yet the 

 pulp-cavity was already partially constricted. 



In position the two teeth lie close to the surface of the gum, and 

 though they overlap the premaxilla they are really external to it, 

 alveoli being imdeveloped \ The anterior one lies just in front of 

 the premaxillo-maxillary suture (fig. 1, ms.), while the smaller pos- 

 terior one lies jnst between the two bones, but under cover of the 

 premaxilla and quite in front of the maxilla. 



In the two cases where only one of these teeth, was developed, it was 

 obviously the anterior one from its position ; it was larger and rounder 

 than the one figured (figs. 1 &. 2, di^), and was evidently younger and 

 still undergoing development. 



The maxillary series of teeth are 5 in number : the first (fig. 1, c), 

 a small uncalcified tooth-germ, which lies close to the anterior border 

 of the maxilla, is obviously the canine ; while the four remaining ones 

 (fig. 1, I., II., III., IV.) represent the deciduous premolars and have 

 not yet developed their fangs. They are simple calcified cappings 

 of the pulp, the only points of interest about them being their 

 proximity to the premaxillo-maxillary suture and the manner in 

 which the first one is displaced so as to partially overlie the second. 



Examining the teeth of the upper jaw as an entire series, we see 

 at once that the most fully formed ones are the two small posterior 

 premaxillary teeth {dr', di^). Unlike the remaining teeth, all of 

 which lie deep down in the bone, these small ones are situated close 

 to the surface of the gum, so that they must evidently cut the gum 

 first if not absorbed. 



A tooth whose crown is once calcified does not, as a rule, increase 

 in transverse diameter, because the dentine composing the greater 

 part of it is deposited from within outwardly ; so that when dealing 

 with a tooth possessing well-marked layers of dentine and enamel, 

 one is fairly safe in saying that the crown will not enlarge much 

 transversely. When the fang is formed and partially constricted at 

 its base, one is justified in regarding that tooth as being fully formed, 

 as the constriction of the pulp-cavity only takes place after the 

 completion of the tooth. 



The small teeth (fig. 2, di^, df), in possessing the above characters, 

 may be safely regarded as having attained their full size and being 

 ready to cut the gum. 



We have now to determine the homologies of these teeth. As 

 we have seen, they are situated in the premaxilla behind the large 

 incisor and immediately in front of the canine. The only teeth they 

 can represent are the 2nd and 3rd incisors ; so that the large incisor 

 is thus proved from its position to be the first or anterior one. 

 From the earlier development and small size of the 2nd and 3rd 



^ Jaeger (JB. nat. Ver.Wiirzb. 1860, xvi.) regards Cuvier's " trous incisifs " as 

 the remainder of a deciduous 2nd incisor ; buL as the 2nd incisor -very i-arely 

 persists and is generally external to the premaxilla, it is improbable that this 

 depression, which is fairly constant, can represent its alveolus. 



