346 DIGESTIVE SYSTEM OF THE HORSE 



pulp-cavity has two principal divisions, and four or three secondary diverticula. 

 The enamel folds correspond, forming a pattern even more complicated than on 

 the upper teeth. 



The Temporary Teeth 

 The deciduous, temporary, or "milk" teeth (Dentes decidui) are smaller and 

 fewer than those of the permanent set. The formula is: 



w 



(3 3\ 

 Di - Dc - Dp - I = 24. 

 3 3/ 



The deciduous incisors are much smaller than the permanent ones. They 

 have a distinct neck at the junction of the crown and root. The crown is short, 

 white in color, and its labial surface is smooth. The infundibulum is shallow. 

 The root is flattened; it undergoes absorption as the permanent tooth develops 

 behind it. 



The deciduous canines are quite vestigial. They occur in both sexes as slender 

 spiculse about a cjuarter of an inch in length, but do not erupt. The lower one 

 develops close to the corner incisor. They are not usually included in the formula, 

 as they are never functional. 



The deciduous cheek teeth differ from the permanent set chiefly in that they 

 have much shorter crowns than the latter. The roots form early, so that a distinct 

 neck occurs. 



The subjoined table indicates the average periods of the eruption of the teeth: 



Teeth Eruption 



A. Deciduous: 



1st incisor (Di 1) Birth or first week. 



2nd " (Di 2) 4-6 weeks. 



3rd " (Di 3) 6-9 months. 



Canine (Dc ) 



Ist^ premolar {Ed 3) 1 ^''^^ «^ ^''^ 



3rd " ::::::::::::::::::::::;::::::(Dp4) j twoweeks. 



B. Permanent: 



1st incisor (I 1) 2}/^ years. 



2nd " (I 2) 3}4 years. 



3rd " (I 3) 41^ years. 



Canine (C ) 4-.5 years. 



1st premolar (or wolf-tooth) (P 1) 5-6 months. 



2nd " (P 2) 21^ years. 



3rd " (P 3) 3 years. 



4th " (P 4) 4 years. 



1st molar (M 1) 10-12 months. 



2nd " (M 2) 2 years. 



3rd " (M 3) 31^^-4 years. 



(The periods given for P 3 and 4 refer to the upper teeth; the lower ones may erupt about six 

 months earlier.) 



THE SALIVARY GLANDS 



This term is usually restricted to the three pairs of large glands situated on the 

 sides of the face and the adjacent part of the neck — the parotid, submaxillary, and 

 sublingual. Their ducts open into the mouth. 



The parotid gland (Glandula parotis) (Fig. 172) — so named from its proximity 

 to the ear — is the largest of the salivary glands in the horse. It is situated chiefly 

 in the space }:)ctwcen the ramus of the mandible and the wing of the atlas. It is 

 somewhat triangular in shape, the apex partially eni})racing the base of the external 

 ear. Its length is al)out eight to ten inches (ca. 20 to 25 cm.), and its average thick- 

 ness nearly an inch (ca. 2 cm.). Its average weight is about seven ounces (ca. 

 200 to 225 g.). 



