38 
EDWAllD B. POULTON. 
general proportion and arrangement is concerned, because the 
shape was most favorable for the movements of mastication, 
which on this theory are supposed to have persisted with little 
change. 
This theory seems to account for all the important facts. 
Few things would give me greater pleasure than to have the 
opportunity of testing it, and of being able to produce an 
exact account of what actually takes place. 
DESCRIPTION OF PLATES II, III & IV, 
Illustrating Mr. Poulton’s paper on “ The True Teeth and 
Horny Plates of O r n i t h o r h y n c h u s paradoxus.” 
PLATE II. 
The upper teeth of both sides are figured iu the series of vertical transverse 
sections forming Pigs. 2 — 15 ; while in Fig. 1 the section, being slightly 
oblique, did not pass through a tooth on the left side. The figures in compart- 
ment a represent sections through the anterior tooth, iu b through the middle 
tooth, and in c through the posterior tooth. In all cases the sections are 
arranged consecutively, Fig. 1 being the most anterior, and Fig. 15 the most 
posterior section; but many sections are omitted. The sections figured were 
selected because they were iu the best condition, and because they were 
suited to show the form aud structure of the various parts of the teeth. All 
the teeth are shown in the natural position, with their apices directed down- 
wards, but of course with their inner sides far more closely approximated 
than iu the natural condition. The drawings were made from Dr. Parker’s 
consecutive sections. All these figures are magnified 1P5 diameters. The 
references are as follows in all the 15 figures. 
e.p. Oral epithelium, d. p. Process of the epithelium passing towards the 
enamel organ aud perhaps the remnant of the neck, which at an earlier date 
connected the latter with the oral epithelium. Ou the other hand there are 
gland-tubes iu close proximity, and many appearances render it probable that 
these may be connected with it. It is seen in sections of the anterior tooth. 
1. Inner layer of enamel organ, the columnar enamel cells, aud the stratum 
intermedium of Hannover. 2. Middle layer of enamel organ. 3. Outer 
layer of enamel organ. D. Dentine, coloured red iu all the figures in which 
it is present. E. Enamel, indicated as a white liue external to the dentine. 
