342 



DIGESTIVE SYSTEM OF THE HORSE 



externally; concave with a median ridge internally; its edges are sharp, and the 

 apex is pointed in the unworn tooth. The root is round and the pulp cavity is 

 large, persisting to advanced age. 



Cheek Teeth (Premolars and Molars). '^ — The constant number of these is 



twenty-four - twelve in each jaw. 



Infundibulum 



Cement 

 Peripheral enamel 

 Dentine 



Central enamel 



Cement 



Lingual surface 



Cement 



Labial surface 



Pulp-cavity 



Quite commonly, however, the 

 number is increased by the pres- 

 ence in the upper jaw of the so- 

 called wolf-tooth. This tooth is 

 usually situated just in front of 

 the first well-developed tooth; it 

 is a much-reduced vestige, not 

 often more than one-half or three- 

 fourths of an inch (ca. 1 to 2 cm.) 

 in length. (It is interesting as 

 being the remnant of a tooth 

 which was well developed in the 

 Eocene ancestors of the horse.) 

 It may erupt during the first six 

 months, and is often shed about 

 the same time as the milk-tooth 

 behind it, but may remain in- 

 definitelj". The occurrence of a 

 similar tooth in the lower jaw — 

 which rarely erupts — increases 

 the dental formula to 44, which 

 is considered the typical number 

 for mammals. Thej- may be 

 regarded as belonging to the permanent set, having no predecessors. The cheek 

 teeth are very large, prismatic in form, and quadrilateral in cross-section, except 

 the first and last of the series, which are triangular. The crown is remarkably 

 long, most of it being embedded in the bone or situated in the maxillary sinus in 



Fig. 



248. — Longitudinal Section of Permanent Incisor 

 Tooth of Horse, About Natural Size. 



Central 



enamel Infundibulum 



Canine tooth 



Fig. 249. — Intiror Tooth or TIorse, Lingual Aspect. 

 (.\fter Ellenl>erger-Bauiii, .\ii:it, fur Kiinstler.) 



Fig. 250. — Canine and Incisor Teeth of Horse. 



The bone has been removed to show the embed- 

 (ieil parts of the teeth. (After EUenberger-Bauin, Anat. 

 fiir Kiiii.stler.) 



the young horse. As the exposetl part wears down the embedded part pushes uj) 

 to replace it, so that a functional crown of about four-fifths of an inch (ca. 2 cm.) 



Mt is common in veterinary works to call all the ohook teeth molars, since, in the horse 

 particularly, the promolurs arc molariform, i. e., do not differ materially from the true molars 

 in size or form. The term cheek teeth conveniently includes the premolars and molars. 



