Royal Institution. 327 



Half the species belong to the old world, which is inhabited by spe- 

 cies of the Legions Euph(xa, Libellago and Calopteryx. The genus 

 Heteerina, containing thirty species, six species of Calopteryx, the 

 genera Heliocharis and Dicterias each containing a single species, and 

 the Legions Amphipteryx and There, are found in America, and prin- 

 cipally in the tropical parts. 



PROCEEDINGS OF LEARNED SOCIETIES. 



ROYAL INSTITUTION OF GREAT BRITAIN. 



February 10, 1 85-1. — Right Hon. Baron Parke, Vice-President, in 



the Chair. 



On the Structure and Homologies of Teeth. By Prof. Owen, F.R.S. 



The Lecturer commenced by observing that, although the teeth 

 were among the least vitalized of animal parts, and commonly pos- 

 sessed no power of repairing fracture or decay, they presented many 

 phaenomena of anatomical, physiological, and homological interest, a 

 selection from which he proposed to oflfer as the subject of the 

 evening's discourse. 



Any hard body attached to the walls and projecting into the cavity 

 of the mouth, where it is exposed to view when the mouth is open, 

 is called a tooth : but the parts properly so called, are those which 

 consist of a gelatinous basis, hardened by earthy salts, in which the 

 phosphate of Ume predomiiiates. Such teeth are pecuhar to the 

 Vertebrate Classes. In them they present manifold varieties as to 

 number, size, form, structure, position, and mode of attachment, but 

 are principally adapted for seizing, tearing, diriding, pounding, or 

 grinding the food ; in some species they are modified to serve as 

 formidable weapons of offence and defence ; in others as aids in loco- 

 motion, means of anchorage, instruments for uprooting or cutting 

 down trees, or for transport and working of building materials ; they 

 are characteristic of age and sex ; and in man they have secondary 

 relations subservient to beauty and to speech. 



Teeth are always intimately related to the food and habits of the 

 animal, and are therefore highly interesting to the physiologist : they 

 form for the same reason important guides to the naturaUst in the 

 classification of animals ; and their value, as zoological characters, is 

 enhanced by the facility with which, from their position, they can 

 be examined in living or recent animals ; whilst the durability of 

 their tissues renders them not less available to the palaeontologist in 

 the determination of the nature and affinities of extinct species, of 

 whose organization they are often the sole remains discoverable in 

 the deposits of former periods of the earth's history. 



Teeth are not of a uniform tissue or substance like bone : that 

 which forms the body of the tooth is called "dentine;" the tissue 

 which forms the outer crust is called '* cement ;" and in most Ver- 

 tebrata a third substance is situated between the dentine and cement. 



