| OCR Text |
Show 442 MR. J. B. SUTTON ON HYPERTROPHY. [May 5, before backwards, and not quite an inch long, and consisted of a small triangular denticle which represented the crown of the tooth, and of a larger part, which for descriptive purposes may be called the fang. The free surface of the denticle was invested with white enamel; subjacent to the enamel there was a well-defined massof dentine which constituted the mass of the denticle. The exterior of the fang was coated with a thin layer of cementum, beneath which there was a thin layer of substance consisting of a granular matrix traversed by numerous canals, which were for the most part arranged perpendicularly to the surface of the fang, so as to extend from the dentine to the cementum. The pulp-cavity was lined throughout the greater part of its extent by a well-defined layer of this substance. The canals visible in this substance probably contained blood-vessels ; in size they approximated to Haversian canals. This substance in all probability is vaso-dentine. Turning, now, to the structural details of an adult specimen of these aberrant teeth, as seen in section (see fig. 8, p. 441), it will become evident, as Prof. Turner has explained, that the peculiar form of this tooth is due to changes in the fang, resulting from an enormous overgrowth of cementum and modified vaso-dentine, the former being produced from the alveolo-dentar periosteum, the latter from the pulp. M y reasons for regarding this singular tooth as a pathological peculiarity are these :- 1st. The elongated portion of the tooth really consists of the fang, and in many animals, even where the teeth do not grow from persistent pulps, there is a great tendency when the crowns are unopposed for the fangs to elongate (hypertrophy). This condition is often very conspicuous in old horses. 2nd. The nutritive conditions of the tooth are exceedingly advantageous for its hypertrophy : not only is it well supplied from the pulp, but its layers of vaso-dentine place it in suitable relation with the alveolo-dentar periosteum. 3rd. Judging from the condition of the crown of the tooth, even in adult Whales, it can be subjected to very little friction. Hence the structure, mode of nutrition, and lack of opposition, place this tooth in a very favourable condition to hypertrophy. Before dismissing teeth, it will be well to point out how simple a matter it is to show that hypertrophy, especially if it be excessive, must almost of necessity lead to dwarfing of the structures more or less associated with it; this is particularly well illustrated in the case of the teeth. In man any tooth differs in size but little from those immediately adjacent; but if, as in the case of rodents, the incisors increase in size, out of all proportion to the neighbouring teeth, their augmentation in volume will lead to a " diversion of the nutrient stream " in their favour, but certainly to the detriment of the teeth immediately succeeding them in the dental series ; and, as a matter of fact, these victimized teeth become so deprived of the essential element-blood, that they remain of stunted size, or have, in some cases, entirely disappeared. It must also be borne in mind that as the incisors increased in size, the effective employment |
