318 Reviews — Prof. H. F. Osborn — Molars of Perissodactyla. 



readers. For this piirpose Prof. Osborn has been good enough to 

 place at our disposal cliches of some of the figures illustrating his 

 memoir; which figures, with some of our own, we reproduce. 



It may be well to premise our observations by stating that the 

 upper molars of the Perissodactyles are constructed on what is 

 known as the lophodont type ; this modification consisting of an 

 outer wall, connected with two more or less nearly complete trans- 

 verse crests inclining backwards. The simplest modification of this 

 type of molar is to be found in the little HyracotJieriiim of the 



'n^^'tn.'^nvef 



Fig. 1. — Left upper premolar and molar teeth of Anchifheriiim [Mesohippus) lairdi. 

 pr. protocone ; pp. posterior prominence. 



London Clay ; but those of the generalized Horse-like animal known 

 as Anchitherium (including Mesohippus) are but little more advanced. 

 Of this genus we reproduce two of Prof. Osborn's figures ; one 

 (Fig. 1) showing the whole series of cheek-teeth, and the other 

 (Fig. 2) a single molar. One species (Fig. 1) is a smaller and simpler 

 form, in which the tubercle marked pp is less developed than in 

 the larger species (Fig. 2). In these teeth there is no difficulty in 

 recognizing the six elements of the sex- 

 tubercular tooth, all of which are indicated 

 by letters in Fig. 2, with the exception of 

 the metaconule, which is the unlettered 

 ridge occupying the middle of the tooth, 

 immediately below the m. The four 

 remaining elements, lettered a. m. p. and 

 pp., have been developed from the basal 

 cingulum surrounding the molar of JSyra- 

 cotherium ; and, accordingly, have nothing 

 whatever to do with the primitive foldings 

 of the crown. This origin is very im- 

 portant with regard to the tubercle marked^ 

 jjp. Thus in Fig. 2 this is so strongly 

 marked as to suggest an origin like the 

 other main tubercles ; but its commence- 

 ment as a slight swelling of the cingulum 

 is clearly shown in Fig. 1. To the 

 elements respectively marked a. m. and 

 pp., Professor Osborn applies the terms 

 anterior pillar, median pillar, and posterior 

 pillar ; stating that the latter term is taken 

 from the writer of this notice, by whom it 

 is said to have been proposed for the teeth 



im'' 



inre 



Fig. 2. — Grinding and 

 outer aspects of a left upper 

 molar of Anchitherium longi- 

 criste. pr. protocone ; pa. 

 paracone ; me. metacone ; hy. 

 hypocone ; pi. protoconule ; 

 a. anterior ridge ; m. middle 

 ridge ; p. posterior ridge ; 

 pp. posterior prominence. 



