Proc. Roy. Socy. of Edin. ] 
[Yol. XXVII. 
Fig. 3.— From a vertical section of the Cranium of a Rat ret. three 
weeks, unweaned. Mother fed on a bread-and-milk diet. The 
photograph shows the frontal bone, and the upper part of the 
nasal septum and nasal cavities. ( x 75.) 
Note the normal state of development of the frontal bone. Cf fig. 4. 
Fig. 4.— From a vertical section of the Cranium of a Rat ret. three 
weeks, unweaned. Mother fed on an ox-flesh diet. For com- 
parison with fig. 3. ( x 75. ) 
Note the imperfect development of the frontal bone and increase in 
the size of the medullary cavity. 
Dr Chalmers Watson. 
[Plate II. 
