260 
A First Study of the Burmese Shell 
The remaining plates illustrate anomalies of conformation found in the Burmese 
cranial series : . 
Plate VII, Fig. 22, skull No. 23 : right temporal bone divided into three separate parts. 
,, Fig. 23, skull No. 136: peculiar ossification in temporal suture. 
„ Fig. 24, skull No. 95 : two pre-condyles fused. 
„ Fig. 25, skull. No. 13: two pre-condyles. 
Plate Vin, Fig. 26, skull No. 113: very deep canine fossae. 
„ Fig. 27, skuU No. 82: os japonicum on L. 
„ Fig. 28, skuU No. 8 : L. upper canine thnist in lateral direction. 
„ Fig. 29, skuU No. 92 : fossa at anterior border of foramen magnum. 
Plate IX, Fig. 30, skull No. 121 : R. os triangulare of interparietal, and ossicle at lambda. 
„ Fig. 31, skull No. 74: long epipteric bone on R. 
Fig. 32, skull No. 103: complete tri-partite interparietal. 
APPENDIX I 
TABLE OF THE OCCIPITAL INDEX 
For the convenience of future craniometrists I have tabled the occipital index 
as obtained from the formula 
Or T - ^ / ^ 
^3' V 24(^3-^3') 
for all values of SJS^' from 1-050 to 1-500; SJSr^' being the ratio of the occipital 
arc from lambda to opisthion, to the chord connecting these two points. 
This index measures the convexity of the occipital bone from lambda to opis- 
thion, giving the ratio of the radius of curvature (supposing the curvature to be 
that of an arc of a circle, which is only roughly the case), to the chord /Sg'. The 
index obviously decreases as greater convexity shortens the radius. 
The value given by our formula is very nearly equal to the index required. Its 
error for a normal proportion like SJS^' = 1-250, say, is only 3 per cent. At 
SJS^' = 1-500 it reaches 5 per cent., and after this point would give a value which 
increases instead of decreasing, with increased convexity. I have therefore made 
SJS^' = 1-500 the limit of my table, and it would indeed be a very abnormal skull 
for which this limit did not suffice. 
