222 Mammalia, 



know the beast to be under eighteen months and oveDf" twelve 

 months old ; from the Molar series we concluded it to be 

 under eighteen months and over nine months old. Hence we 

 may certainly conclude the animal before us to have been 

 from twelve to eighteen months old*. 



Examination of the Developing Tooth and others. 

 By removing the capsule around the posterior tooth of the 

 Molar series, the different structures of a tooth may be made 

 out. The soft pulpy material at the base is the Dental pulp, 

 a soft, highly vascular, and sensitive substance, accurately 

 filling the central cavity of the tooth. The lower paTt of the 

 solid portion of the tooth is composed of Dentine, which 

 forms the principal mass or foundation of the body of the 

 tooth, gives the general form, and immediately encloses the 

 cavity. The upper part is formed of Enamel. It will be well 

 now to remove this Tooth and place it in a solution consisting 

 of two parts of Nitric Acid and one part of Chromic Acid in 

 one hundred parts of water, with a view to making a longi- 

 tudinal section through the tooth when it is soft enough to 

 admit of cutting, to show the external coating of enamel, the 

 inner coat of dentine, and the central pulp cavity in their 

 relative positions. 



"We may note here, as in all Ruminants, that the outer 

 contour of the entire Molar series is slightly zigzag, the 

 anterior and outer angle of one tooth projecting beyond the 

 posterior and outer angle of the next in advance ; also, that 

 in most of the deciduous series, but in the three posterior 

 teeth onlyf of both upper and lower jaws in the perma- 

 nent series {i.e., the True Molars), may be seen the character- 

 istic complexity of the Ruminant grinder ; the grinding 



* The Head under dissection having been purchased in September, it is 

 probable that the lamb was born late, about March. 



t The three first or premolars have, as before said, more simple crowns than 

 those which they displace. 



