42 MR. M. F WOODWARD ON THK [Jan. 5, 



incisors it is highly improhable that they could persist after birth, 

 whence we may reasonably look upon them as destined to be in all 

 probability either absorbed or shed in utero. 



Giebel and Brandt, as already mentioned, have described two 

 Incisors on either side of the upper jaw of young animals, and it 

 seems, therefore, probable that the 2nd incisor may persist occasion- 

 ally, especially as in two of my preparations, where only one of these 

 teeth was present, the second incisor had undergone an increase in 

 size, although it had not yet developed a fang ; in fact, it was much 

 more in the condition of "the other milk-teeth, being more normally 

 developed. It will be observed from this that there is nothing which 

 will justify the unqualified assertion of Giebel and others before 

 alluded to, that two upper incisors normally exist in the permanent 

 dentition ; for these small teeth never, I believe, persist till the 

 permanent teeth appear ; although they are only represented in one 

 dentition, I incline to the belief that they should be regarded as 

 milk-teeth. 



In the lower jaw (Plate II. fig. 1), in addition to the 2 typical in- 

 cisors and 4 premolars, we find on either side a small well-developed 

 tooth (fig. l,c) situated between the incisors and the first premolar. 

 It lies close to the surface of the gum and is intermediate in size between 

 the two vestigial upper incisors, measuring '4 millim. long X '3 

 millim. wide, and is correspondingly well developed (tig. 2, c). It 

 possesses well-marked enamel and dentine layers to the crown and a 

 small simple fang. Like the small teeth in the upper jaw, its parts 

 are all fully developed ; but it is so small that, as in the case of the 

 3rd upper incisor, it has never before been observed. It certainly 

 never persists after birth, even if it ever cuts the gum at all. 



When the jaws are closed, this tooth is situated just between the 

 upper canine and the third upper incisor, a position which suggests 

 that it is the lower canine ; but it is so close to the lower incisor 

 that it might very well be the missing tooth of that series. 



When, however, we note the order of suppression going on iu 

 the upper jaw, we find that while the two posterior incisors rarely 

 persist, the canine is occasionally present even in the second dentition ; 

 this suggests that the latter is not so fully reduced as the incisor, 

 wherefore we might, by analogy, fairly expect to see the canine more 

 pronounced in the lower jaw. Further, recent observers ' find in the 

 Rhinoceros, one of the immediate allies of Hyrax, where only one of 

 the anterior series of mandibular non-cheek teeth remains, that that 

 is in all probability the canine and not an incisor. 



From argument by analogy, I am therefore inclined to regard 

 this small disappearing tooth as the lower canine, the 3rd and pos- 

 terior incisor having apparently completely disappeared. 



From the foregoing it may safely he concluded not oidy that the 

 canines have, in Hyrax, ceased to have any functional importance, 

 but that the incisors are being reduced in number by the suppression 

 of the posterior ones. 



In the permanent dentition the first premolars, both above and 

 1 Lydekker, in Flower & Ljdekker (9). 



