THE TEETH 339 



first incisor, and may be conveniently indicated by the notation V. The tem- 

 porary or deciduous teeth may be designated in a similar manner, prefixing D 

 (for deciduous) to the letter indicating the kind of tooth. In addition to the above 

 systematic method of notation other terms have received the sanction of popular 

 usage. Thus the first incisors are commonly called "pinchers," or "nippers"; 

 the second, intermediate; and the third, corner teeth. The canines, when highly 

 developed, may be termed tusks or fangs. The vestigial and inconstant first 

 premolar of the horse is popularly termed the "wolf tooth." 



Each tooth presents for descri])tion a portion coated with enamel, termed the 

 crown (Corona dentis), and a portion covered with cement, termed the root (Radix 

 dentis). The line of union of these parts is the neck (CoUum dentis).^ In many 

 teeth the neck is distinct and is embraced by the gum, e. g., the teeth of the dog 

 and the temporary incisors of the horse. In other teeth no constriction is seen, as 

 in the permanent incisors of the horse. Between these extremes may be noted 

 the molars of the horse, in which the neck is seen only in advanced age. 



The surface of a tooth directetl toward the lips is termed labial ; toward the 

 cheek, buccal; and toward the tongue, lingual (Facies labialis, ]:)uccalis, lingualis). 

 The surface oi^posed to a neighboring tooth of the same dental arch is termed the 

 contact surface (Facies contactus). The grinding or masticatory or "table" 

 surface (Facies masticatoria) is that which comes in contact with a tooth or teeth 

 of the opposite jaw. 



Structure. — Teeth are composed of four tissues, which are considered here 

 from within outward. The pulp (Pulpa dentis) is a soft gelatinous tissue, which 

 occupies a space in the central part of the tooth termed the pulp cavity (Cavum 

 dentis). The pulp is well supplied with blood-vessels and nerves. It occupies 

 a relatively large s])ace in young growing teeth, but later the dentine deposited 

 on its surface gradually encroaches on it until, in advanced age, the cavity is 

 obliterated or much reduced. The dentine (Substantia eburnea) forms the bulk 

 of most teeth, covering the surface of the pulp. It is very hard, and is yellowish- 

 white in color. The enamel (Substantia adamantina) constitutes a layer of varying 

 thickness covering the dentine of the crown of the tooth. It is easily distinguished 

 by its clear bluish-white appearance and its extreme density. The cement 

 (Substantia ossea) is always the outermost tooth substance. In simple teeth it 

 forms usually a thin layer on the surface of the dentine of the root only, but in com- 

 plex teeth it exists in considerable quantity, tending to fill in the spaces between the 

 enamel folds of the crown also. Its structure is practically the same as that of 

 bone without Haversian canals, and even these occur where the cement forms a 

 very thick layer. The embedded part of the tooth is attached to the alveolus by 

 a vascular layer of connective tissue, the alveolar periosteum (Periosteum alveolare), 

 which constitutes the periosteum at once of tooth and alveolus. 



The blood-supply to the pulp is derived from the alveolar or dental branches 

 of the internal artery ; the nerve-supply comes from branches of the trigeminus. 



^ It will be noted that this definition of crown and root does not agree exactly with the 

 popular view that the crown is the free portion and the root the embedded portion. The objec- 

 tion to the latter statement lies in the fact that it is not capable of general application. Thus 

 the morphological crown of the permanent molars in the horse is extremely long, and is, for the 

 most part, embedded in the bone in the young animal. The root proper laegins to form at four 

 or five years of age, and continues its growth for about eight years. As the exposed part of the 

 crown wears down, the embedded part pushes out of the alveolus, thus preventing deficiency of 

 length. On the old basis we should have to say that successive portions of the root become 

 crown, while in point of fact it is only in very extreme age that the true root comes into wear. 



