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Show 1892.] MILK-DENTITION OF PROCAVIA CAPENSIS. 39 of Hyrax (viz., the Rhinoceros, Tapir, and Horse), which never possess more than seven cheek-teeth (molars and premolars), while showing all stages in the development of the canine. He has succeeded in showing that many of the earlier observers figured and described these canines, mistaking them for the 1st premolars, on account of the resemblance between the latter in the second dentition and the milk-canines. But although the 1st premolar in the second dentition is much reduced and has sometimes only one fang, it is situated some distance from the premaxillo-maxillary suture, and in the first dentition has a large crushing crown and is two-fanged. He considers that the canines, together with the 1st premolar, are undergoing suppression, and that as a consequence of this the former teeth have lost their more typical characters. With the exception of Giebel (12, 13) and Brandt (2), all observers state that there is only a single pair of incisors in the upper jaw. These two authorities, however, have described in the young animal a second small and posterior incisor, which is early shed and is situated in the premaxilla behind the large first milk-incisor. This tooth is not to be confounded with the milk-incisor No. 1, which is a large tooth situated between the two permanent ones, as figured by Cuvier (5) and Blainville (1) ; it undoubtedly represents a 2nd upper incisor, although in all probability it is only a milk-tooth, always present in the fcetus, but seldom, I believe, persistent after birth. Giebel and Brandt were of opinion that Cuvier mistook these small incisors for canines ; but as the former are situated in the gum which covers the premaxilla, while the latter lie well within the maxilla, their position implies that he did not understand what is generally supposed to be the fundamental distinction of the canine, viz., that it is typically a single-fanged pointed tooth implanted in the maxilla just behind the premaxillo-maxillary suture. It has been already noted that no observer has seen more than 9 teeth in the upper jaw; none of those who describe the presence of a canine make the slightest allusion to the presence of 2 upper incisors, and further perusal of the descriptions alluded to shows that those who described the 2nd incisor almost certainly were dealing with Cuvier's canine. This is probably due to the fact that the earlier observers do not seem to have had access to some of the monographs of their predecessors, but it does not excuse a modern European writer like Lataste having apparently failed to consult a classical work like Brandt's Monograph on Hyrax, or a standard one such as Bronn's ' Thier-Reich.' II. Besults of the present Investigation. The material which I have examined was kindly placed at my disposal by Prof. Howes, and consisted of 5 fcetal examples of Hyrax capensis preserved in spirit, being the specimens the placenta of which was described by Prof. Huxley before this Society in 1863 \ The 1 P. Z. S. 1863, p. 655. |
