British Journal of Dental Science. No. 311. LONDON, JANUARY 1, 1881. VOL. XXIV. A COURSE OF LECTURES ON DENTAL ANATOMY AND PHYSIOLOGY. Delivered at the National Dental College during the Winter By THOMAS GADDES, L.D.S. Eng. Lecturer also on the Elements of Histology; Assistant Dental Surgeon to the National Dental Hospital. LECTURE I. GENTLEMEN,-Our study of the anatomy and physiology of the teeth will be conducted in a manner which I have considered as perhaps the most systematic. With the endeavour to present the subject before you in as comprehensive and connected manner as possible I shall not regard the presumptuous animal-man-as possessing the typical or ideal dental apparatus; but by surveying the animal kingdom, in which man finds a place, we may obtain numerous examples of progressive development and adaptation of dental organs for those purposes which best fulfil the requirements of the several groups of animals. Then by studying the structure and functions, distribution and development of the dental tissues and organs, I shall aim to supply as best I can, a Synthetic Study of Odontology. To build up this subject strictly in that manner would, in the present state of our knowledge, be impossible. The object of these lectures being to impart information and to teach, rather than to set forth any flowery elocution at the expense of your time and of the duty undertaken by me, it will occasionally be expedient to resort to an analytic method of inquiry, so that our investigation into the more simple forms will be thereby facilitated. As we shall have to study different members and groups of the animal kingdom, it will be advantageous to give you some general plan of the classification of animals, and the one here set forth is based upon the structure and function of the creatures so arranged; therefore it is termed a "morphological classification." The orders, genera, and species are not fully worked out in the following tables, but the details will be found sufficiently complete for our present purpose: VOL. XXIV. 1 Mollusca propria Lamellibranchiata (Mussels, Cockles, Oysters). Gasteropoda Sub-class. {Branchiogastropoda (va, elks, Periwinkles, Sea Slugs). Pteropoda ("Butterflies of the deep "). (Slugs, Snails). The animals lowest in the scale of organisation, which belong to the class Gregarinide and to the sub-kingdom Protozoa, are devoid of mouths and digestive apparatus. They live entirely by imbibition or osmosis; and in the adult state they have not the power of emitting pseudopodia. The animals may be found in the intestine of the cockroach, earth-worm, &c. In the next class, the Rhizopoda, are animals which possess the power of throwing out processes of their substance, as white blood-corpuscles do, and of exhibiting distinct amoeboid movement. These processes are called "pseudopodia" or false feet. There is neither mouth nor anus; but by means of the pseudopodia becoming attached to and encircling nutritive particles, and drawing them into its substance, does the animal perform the function of ingestion or feeding. Any part of the surface is capable of performing this function. When a particle of food has passed into the body the aperture by which it entered immediately closes up, and the discharge of solid excreta is effected in a similar manner, except that only one portion of the general surface appears to be limited to this excretory purpose. In the substance of many of these lowly creatures nothing is to be discerned but a mass of jelly-like substance resembling a particle of thin glue. As we ascend the scale of organisation and come to the higher class of Protozoa-the Infusoria-there is to be found a mouth, a rudimentary digestive cavity, and an anus. The mouth leads into a funnel-shaped gullet which opens into the soft central mass of sarcode. The food passes into this body substance, and not into any definite stomach, where it is digested. The anus is situated close to the mouth, but is only seen when in use. In the sub-kingdom Celenterata, the members of the lower class-Hydrozoa-which contains the fresh water polyps, possess a permanent mouth and body cavity, the mouth communicating with the body cavity. In the higher class Actinozoa, which includes the sea-anemones, so common in aquaria, there is, in addition to the body cavity, a distinct stomach. The mouth leads into the stomach, which is a wide membranous tube, opening by a large aperture into the body cavity, but there is no distinct alimentary canal nor anus. A Hydrozoon or Hydra, is essentially an open-mouth saccule, consisting of two membranes, an outer or ectoderm, and an inner or endoderm. The majority of these animals seize their prey by means of tentacula, which are processes of those membranes developed either around the mouth or from the walls of the digestive cavity. |