CHAP. IX.] TEETH: CANIDiE. 211 



3 — 3 



20. Absence of incisor is very rare in Dog. One case of i- — given by 



Hensel, I. c. p. 534. (Hensel observes that this gives the formula for 

 incisors of Enhydris \Latax\ ; he also calls attention to fig. of Enhydris 

 with three lower incisors in Owen, Odontogr., PL 128, fig. 12, but as 

 this is not mentioned as an anomaly in text, it is very doubtful.) 



21. Dog having the upper canine imperfectly divided into two on 

 each side as shewn in Fig. 39. The plane of division was at right 



Fig. 39. Right and left profiles of Dog having the canines partially divided. 



angles to the line of the alveolus so that the two parts of each 

 canine stood in the plane of the series of teeth. The division was 

 more complete on the right side than on the left. The lower 

 canines were normal. This sjiecimen was kindly sent to me by 

 Mr J. Harrison. 



II. Variation in Premolars. 



Several distinct variations were found in the premolars of 

 Canidse. A number of cases shew five upper premolars instead 

 of four, and the question then arises whether the extra tooth is 

 due to the division of a single tooth, or to reconstitution of the 

 series 1 . The occurrence of a fifth premolar in the lower jaw is 

 much rarer, only three or four cases (Wolf (2) and Greyhound (? 2)) 

 being known to me. The following other forms of Variation oc- 

 curred. In C. mesomelas, No. 228, an extra tooth stood internal 

 to p^, and was perhaps a duplicate of this tooth. One case of 

 bifid p^ was seen, and two cases in which $P had apparently 

 divided to form two single-rooted teeth (C. viverrinus, No. 227 

 and a Sledge-dog, No. 237). A few examples of absence of p 1 

 deserve notice. Lastly, though really an example of Substantive 

 Variation, I have included a curious case of possibly Homceotic 

 variation of yP_ into the partial likeness of the carnassial (No. 245). 



1 On this point see Chapter x. Sections 3 and 5. 



14—2 



