40 MR. M. F. WOODWARD ON THE [Jan. 5, 



specimens measure about 12-5 centim. long and only show a few of 

 tlie larger hairs. 



The method adopted for the examination of the teeth is, I believe, 

 the only reliable one (if employed in connexion with serial sections) 

 by which the true relations of developing teeth in a young animal 

 can be made out. 



The skin was carefully removed from the sides of the jaw, and 

 the whole jaw, with gum covering it intact, was placed in absolute 

 alcohol and thoroughly dehydrated ; it was then clarified in clove-oil, 

 and either examined in that medium or mounted in Canada balsam. 

 By this treatment the teeth are seen through the bones in their 

 natural position in relation to one another and to the surrounding 

 parts, whereas by dissection they are apt to be displaced. Further, 

 some teeth when undergoing suppression are so minute as to be 

 practically invisible to the unaided eye, so that under manipulation 

 by ordinary dissection they would be entirely overlooked. On the 

 other hand, if exclusively examined in serial sections it is doubtful 

 if their exact position and relationships could be determined with 

 absolute accuracy. This is notably the case with the anterior milk- 

 incisors ot the Rabbit (the upper of which measures only 'IS milHm. 

 in length) described by Huxley (16) (figs. 4 & 5, di^), and which 

 were discovered by this method, Huxley being, I believe, the first to 

 apply it to the examination of tooth relationships. 



It is worthy of note that the method does not prevent one after- 

 wards sectionizing the jaw ; in fact, it is best to examine the jaw 

 first in this way in order to see exactly what teeth are present and 

 what are their positions, as it then becomes much easier to interpret 

 the appearances presented by serial sections. 



A microscopic examination of the clarified jaw (Plate II. fig. 1) 

 shows that there are present at this age 8 teeth in the upper jaw and 

 7 in the lower one. 



Those of the upper jaw may be divided into premaxillary and 

 maxillary teeth, there being 3 of the former (fig. 1, di\ df, df) 

 and .5 of the latter (fig. 1, c, i., ii., iii., iv.). The first pre- 

 maxillary tooth is very large and roughly conical ; it lies completely 

 buried in the bone and, from a comparison of a series of skulls, it 

 becomes evident that it is the milk predecessor of the large permanent 

 incisor; it attains a considerable size and persists for a long period after 

 birth. As the foetus was very young, the permanent incisor had 

 not yet been differentiated. 



The two posterior premaxillary teeth (fig. 1, di^, df) are very 

 siTiall, and variable ; both were present in three out of six preparations, 

 one only was present in two, and both were wanting in the other. 



In two cases they were very fully developed (fig. 2, df, df), although 

 small, and the anterior one was in all cases the largest. In the speci- 

 men figured the measurement of the anterior one (df) is "62 millim. 

 long X "35 millim., that of the posterior one (df) being "31 millim. 

 long X '19 millim. 



The anterior one presents a small conical crown composed of a 

 distinct layer of enamel and dentine (fig. 2, df, c, and d), a well- 



