398 A Stud;/ of the Nasal Bridge in the Anthropoid Ap>es 
That is, it is of the order of the probahle error. It may amount to 1'7, which 
is only about twice the probable error when we combine the effect of random 
sampling with personal error. 
(ii) The differences in the mesodacryal index ft can amount for personal 
variation to 4'2 (Congo $ 's), which is as large a value as we obtain on the 
Egyptian series for combined personal error and random sampling, and even to 
6"6 points in the Whitechapel with change of sample and personal variation, 
which is five times the probable error. Corresponding differences will of course 
exist in a deduced from /?. We believe that this difference in the early and 
late values of (3 is due to greater standardisation of method in determining the 
dacryon with a rather blunt pointed instrument and to greater mastery of the 
difficulties arising from damaged crania and in the case of the apes from partially 
obliterated sutures. 
(iii) In the absolute measurements mesodacyral chord {DC), mesodacryal 
subtense (DS), mesodacyral arc (DA), simotic chord (SO), simotic subtense (SS) 
there is a maximum error in the means of about 4 - 5°/ o , but this is rare, and 
reduces to insignificance with practise in the measurements*. 
(iv) A comparison of B and G shows that in all cases after continuous 
practise and standardisation of method, the variations in absolute measurements 
or in indices are less than the probable errors of random sampling. 
Of course the whole of the above remarks apply to a comparison of mean 
values and not to measurements on an individual cranium. We should conclude 
as follows : 
(a) The measurements on the nasal bridge need great care, and the same 
measurer may on repetition differ considerably from a previous determination on 
the same skull. 
(b) But with long practise and careful standardisation of method the racial 
values obtained will repeat themselves, if the series be measured afresh, and 
values obtained by the same recorder are quite intercomparable. 
(c) We are doubtful — especially having regard to Merejkowsky's results — 
whether racial values obtained by different craniologists, who are fresh to this 
side of cranial measurement, or who have not tested their personal equation on 
the same series, will be directly comparable. 
(d) Notwithstanding these difficulties, which are really only an intensifica- 
tion of difficulties which occur in all branches of craniometry, we believe these 
measurements on the nasal bridge to be really valuable and think that they 
ought to occupy more attention. They are of course only a phase of what may 
reach greater importance in the future : namely of what we may term micro- 
metric as distinguished from the usual or macro-metric measurements of the skull. 
* The earlier series of measurements tended rather to exaggerate the mesodacryal chord 
and arc. 
