114 
Brain-weight and Head-size 
D 
Fig. 4. Four horizontal sections through the frontal bone, showing the condition of the bone at 
various ages. 
A. Male, aged 9. Bone thin, no frontal sinuses. 
B. ,, ,, 14. Bone considerably thicker, no frontal sinuses. 
C. ,, ,, 32. Illustrating the occasional absence of the frontal sinuses in an adult. 
D. ,, 54. Unusually large frontal sinuses. 
From specimens in the Museum of the Eoyal College of Surgeons, London. 
