936 



THE ORGANS OF DIGESTION. 



There is an anatomical correspondence between the forms and arrangement 

 of the teeth, the form of the condyle of the inferior maxilla, and the mus- 

 cular arrangement. Individuals who have teeth with long cusps have the head 

 of the bone much rounded from before behind, and have a preponderance of 

 the direct over the oblique muscles of mastication, and vice versd ; teeth with 

 short or no cusps are associated with a flattened condyle and strong oblique 

 muscles. 



Very great aberrations in the dental arrangement are frequently followed by 

 accomodative changes in the heads of the inferior maxilla. 



Structure of the Teeth. 



The Dental Pulp. A longitudinal section of a tooth will show the presence of a 

 central chamber having the general form of the crown of the tooth. Processes of 

 the chamber pass from its body, one for each root and down each root, and open at 



Pulp 

 cavity. 



Root. 



FIG. 560. Vertical section of a molar tooth. 



the apex by a minute orifice, the apical 

 foramen. This cavity is known as the 

 pulp-chamber, the minute canals the 

 pulp-canals. The cavity contains a soft, 

 vascular, and sensitive organ called the 

 dental pulp. It is made up of myxoma- 

 tous tissues, and contains numerous blood- 

 vessels and nerves, which enter by way 

 of the apical foramina. It does not pos- 

 sess lymphatics. The periphery of the 

 pulp is bounded by a layer of cells ar- 

 ranged like columnar epithelium, each 

 cell sending one or more branched pro- 

 cesses through the basic substance of the 

 dentine. These are the dentine-forming 

 cells, the odontoblasts of Waldeyer. The 

 blood-vessels break up into innumerable 

 capillary loops which lie beneath the 

 layer of odontoblasts. The nerve-fibrils 

 break up into numberless non-medullary 

 filaments, which spread out beneath the 

 odontoblasts, and probably send terminal 

 filaments to the extreme periphery of the 

 pulp outside the odontoblasts. 



The matrix cells and their processes 

 are irregularly arranged in the body of 

 the pulp, but in the canal portion the 

 fibrillse are in the direction of the axis 

 of the root. 



The section will exhibit three hard tissues in a tooth, one forming the greater 

 mass of the tooth ; hence its name dentine (the ivory). The dentine upon the 

 crown is sheathed by a layer called the enamel ; the dentine of the root is enclosed 



FIG. 561. Vertical section of a tooth in situ (15 

 diameters), c is placed in the pulp-cavity, opposite 

 the cervix or neck of the tooth : the part above is the 

 crown, that below is the root (fang). 1. Enamel with 

 radial and concentric markings. 2. Dentine with 

 tubules and incremental lines. 3. Cement or crusta 

 petrosa, with bon corpuscles. 4. Dental periosteum. 

 5. Bone of lower jaw. 



