JOURNAL OF MICROSCOPICAL SCIENCE. 



EXPLANATION OF PLATES VI & VII. 



Illustrating Dr. Rollcston's paper on the Development of the 

 Enamel in the Teeth of Mammals^ as illustrated by the 

 various Stages of Growth demonstrable in the Evolution 

 of the Fourth Molar of a young Elephant, Elephas indicus, 

 and of the Incisor Teeth in the Foetal Calf, Bos taurus. 



DESCRIPTION OP PLATE VI. 

 Fig, 1. Portion of left half of lower jaw of young Elephant, Elephas 

 indicus, showing the fourth molar in course of development, and a part of 

 the third molar, some of the denticles of which were in use, and some still 

 within their socket. The teeth are seen from the inner side, the bony wall 

 having been removed, and the capsule of the posterior tooth having been 

 reflected. The dentinal pulp is coloured blue, the dentine yellow ; the 

 vessels are represented as seen when filled with a red injection. From a 

 preparation made by Mr, C. Robertson. 



a. Part of inner side of lower jaw interposed between the posterior 



denticles of the third and the anterior denticles of the fourth molar. 



V^. Part of third molar tooth. Its anterior denticles were in use ; some 



of its more posteriorly placed were just about to cut the gum, and 



the most posteriorly placed were still within the bony socket. 



b^. Processes of dentinal pulp, dividing to supply the denticles of third 



molar. 

 c. Sac of tooth reflected and fastened out over the jaw above and below, 

 «?', dr, d^. Capsular processes surrounding denticles. On the internal or 

 dentinal aspect of the most anteriorly placed of these (c?'), a granular 

 deposit is observable. This deposit corresponds to a deposit {g^), 

 of similar appearance, which encrusts the upper part of the cap of 

 dentine (/*), and it represents the proximal ends of the enamel 

 columns which have broken away from the more perfectly calcified 

 segments which constitute the (enamel) deposit {g^), on/*. 

 <?*, (?-, e^, e'*, e". Processes of the dentinal pulp passing up to form the 



successive denticles of which the composite molar is made up. 

 e^. A number of processes homologous with those similarly lettered, but 

 diiFering from them in having as yet formed no cap of dentine upon 

 their exterior surface. 

 /S /'j /^ /■*» P- Caps of dentine which have been formed by the pro- 

 cesses of dentinal pulp (e^ e", ^, e^, e^). Upon the three most 

 anteriorly placed of these caps of dentine (f^,/',/^), a deposit of 

 enamel has taken place, the area occupied by which diminishes in 

 length from before backwards, in correspondence with the lessening 

 evolution of the denticles. Upon the two most posteriorly placed 

 (/^, /^), of the dentinal caps no deposition of enamel has as yet 

 taken place, 

 g^, g^, g^. Level to which the deposit of enamel has reached upon the 

 dentinal caps (/S/^,/^), respectively. 



DESCRIPTION OF PLATE VII, 



Fig. 2, Section of anterior portion of lower jaw of foetal calf. Bos 

 taurus, taken in an antero-posterior or sagittal direction; showing the 

 enamel organs of two teeth, one larger and the other smaller, in situ. 

 The section has passed through the lateral portion of each tooth ; and as 

 the incisors in this species have their crowns laterally expanded, whilst their 



