THE DECIDUOUS TEETH—ERUPTION OF THE TEETH 403 
closed by deposit of cement. The pulp-cavity has two main divisions (anterior 
and posterior) and three or four secondary diverticula. The enamel folds corres- 
pond, forming a pattern even more complicated than on the upper teeth. On 
the exposed crown of the unworn tooth the enamel folds form rounded ridges 
covered with a thin layer of cement. After the tooth comes into wear the enamel 
on the masticatory surface stands out in the form of sharp, prominent. ridges.’ 
Progressive cementation of the periphery of the tooth takes place, thus leveling up 
the irregularities of surface to a considerable extent. 
The lengths of the lower teeth shown in Fig. 342 were in centimeters: 5.7, 7.9, 9.0, 8.5, 8.2 
7.6. The distance between the two rows was 4.7 cm. at the anterior end and 7 cm. at the posterior 
end. 
THE DeEcIbUOUS TEETH 
The deciduous teeth are smaller and fewer than those of the permanent set. 
The formula is: 
3 0 33 
2 (Pi; de—po) = 
33 0 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 
spicule about a quarter 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 premolars 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. 
Vessels and Nerves.—The blood supply of the teeth is derived from the 
infraorbital and alveolar branches of the internal maxillary artery. The lymph 
vessels go to the mandibular and pharyngeal lymph glands. The nerves come 
from the trigeminus. 
ERUPTION OF THE TEETH 
The subjoined table indicates the average periods of the eruption of the teeth: 
TEETH ERUPTION 
A. Deciduous: 
Stan CISOnseee-& Bee cia tls Se en eee eas (Di 1) _ Birth or first week. 
OATG [ew SOO ear ey ere bee tke eet eee (Di 2) 46 weeks. 
BUG A” es Be I ane i a an eee eae ene (Di 3) 6-9 months. 
Canine. . LS ag rae ee ee (De ) 
Sts PLM OLB a ee hapes a tassios re sake nyse 22 cise SE (Dp 2) . - 
CATA EGY eine as PR A he ee ee (Dp 3) | Bieeoe tree 
Sra SAIN ey Sa ates Sos 6 ee ee Ophea) ss 
B. Permanent: 
ES ISO sees eo a ea ee eee (11) 216 years. 
Chis |, aa Se ee oe Se eee) ee eee hee (12) 3) years. 
SECM ae eo SNS eh oe 2 cla SRN tore Ses (13) 416 years. 
Canine teehee ee ce cs cee eee cae os (C) 4-5 years. 
1st premolar (or wolf-tooth).................. (P1) 5-6 months. 
PATE N oe LS Ta Cee ee tee ae ae ee eee (P2) 216 years. 
3rd SEP ora eer singe aie SES (P3) 3 years. 
4th Moe ean Gale SERED RE Ree nee (P4) 4 years. 
sGarm Olas srateeias see te net. eee (M1) 10-12 months. 
PAU Re een i ed ee ee eS ee (M2) 2 years. 
Somos eta cs Stes ete. pate pee srg UTS (M3) 31644 years. 
(The periods given for P 3 and 4 refer to the upper teeth; the lower ones may erupt 
about six months earlier.) 
_ 1 It is estimated that the enamel ridges of an upper cheek tooth of a young adult horse, if 
straightened out, would form a line more than a foot long. The extent diminishes with age. 
