The author has already proposed a method for the discrimination of five vowels by machine lip reading. However, the influence of coatriculation between vowels is very important for word recognition. This paper first describes a method of lip reading for the concatenation of two vowels. The discrimination rate is 98.2%, which means that coartriculation evaluation is very effective compared with the discrimination method which evaluates each vowel respectively. Secondly, the influence of coartriculation on each vowel concatenation is discussed, based on the Maharanobis' generalized square distance for double vowels i. e., 'aa' 'ee' 'ii' 'oo' 'uu'. Finally, this lip reading method for the vowel concatenation is applied to the recognition of digits "zero" through "nine". In the discussion, the optimal vowel expression of the digits for machine lip reading is described.