622 THE EXTERIOR OF THE HORSE. 



with the eruption of the first permanent molars. Their alveoli are, in fact, 

 placed immediately in front of these teeth; we have, nevertheless, seen examples 

 in the inferior jaw in which the supplementary teeth and the first permanent 

 molars were separated by a space of three centimetres. Finally, they persist 

 sometimes in very aged horses. 



Their presence renders the dental formula somewhat variable. 



Elongated and slightly curved upon itself in the direction of its length, the 

 supplementary premolar resembles, by the form of its free part, the incisor of 

 a carnivorous animal. It is for this reason that certain authors have given it 

 the name wolf tooth. Its incased extremity is unicuspid. One of these teeth, 

 measured in a horse six years old, had a length of 0.025 m. 



As to the posterior supplettientary molars, which Girard has simply mentioned, 

 we have never seen them ; it is probable that he has mistaken certain anomalies 

 for such teeth. We will further refer to these anomalies. 



2. The Molars Proper. 



They form the lateral parts of the dental arcades, and are distinguished, like 

 the incisors, according to their epoch of eruption, into molars of the first and 

 of the second dentition. 



We will commence our study with the former. 



A. — Molars of the First Dentition. 



There are twelve deciduous milk molars, or molars of the first dentition : six 

 in each jaw and three on each side. It was believed for a long time, upon the 

 authority of Ruini,^ that they were only eight in number ; Tenon has demon- 

 strated that this is an error.^ 



These teeth, strong and short, have the general form of a quadrangular 

 prism, save the first, which has only three faces. 



They present four faces and two extremities. 



Faces. — The anterior and posterior faces, almost plane, show nothing re- 

 markable ; but in the first tooth, above as well as below, the anterior face is 

 replaced by a border of no great thickness ; it is the same for the posterior face 

 of the third inferior molar. 



In the superior jaw, the external face, FE, has three grooves in the first 

 and two in the second and third (Fig. 293). 



The internal face, FI, irregular, very slightly concave in the direction of 

 its length, presents gutters much less distinct. 



In the inferior jaw (Fig. 294), the external face, FE, shows, in the middle 

 of its length, a groove which augments in depth and diminishes in width from 

 the first to the third molar. 



The internal face, FI, almost plane, is irregularly grooved. 



Each of the deciduous molars is provided, at the level of its root, with a 

 constriction or neck rather well marked and completely encircling the tooth. 



Extremities. — 1st. Incased Extremity. — The inferior molars have two roots, 

 the one anterior, the other posterior. They are strong, convex externally, and 



1 Anatomia del Cavallo, by Carlo Ruini, Venice, 1598. 

 * Tenon, loc. cit., p. 60. 



