Still another example of fixity of type is presented in the woven bags of the Ojibwa and Potawatomi (figs. 149, 150). The two opposite sides have always distinct patterns. The purely geometrical patterns are always laid out symmetrically. There is a broad central figure bordered by a number of narrow stripes. These are followed, above and below by a wide stripe of a pattern different from the central one. Sometimes the colors above and below are inverted. The dividing line runs all around the bag, but the patterns in the broad bands change. On the one side there are often representative figures above, and in this case there is no correspondence between the upper and lower designs. Similar bags are used by other neighboring tribes. The Potawatomi use the same decorative arrangements, except that the central band often remains undecorated.[96] [96] See Alanson Skinner, The Mascontens or Prairie Potawatomi Indians, Bull. Public Museum of the City of Milwaukee, Vol. 6, No. 2, Plate 21. [Illustration: Fig. 149. Design from pouch, Ojibwa.] [Illustration: Fig. 150. Design from two sides of pouch, Potawatomi.] [Illustration: Fig. 151 _a_. Type of parfleche and pouch painting, Arapaho.] For a clear understanding of the character of a local style a comparison with related forms in contiguous areas is indispensable. Historical conditions like those that may be traced in the development of art forms in prehistoric and historic times in Europe and in Asia have been determinants in forming the art of primitive people also. There is probably not a single region in existence in which the art style may be understood entirely as an inner growth and an expression of cultural life of a single tribe. Wherever a sufficient amount of material is available, we can trace the influence of neighboring tribes upon one another, often extending over vast distances. Dissemination of cultural traits that has made the social structures, the ceremonials and the tales of tribes what they are today, has also been a most important element in shaping the forms of their art. The local distribution of technical processes, of form elements, and of systems of arrangement contribute to the character of each art style. In another place we have discussed the distribution of pottery decorated by means of applied pellets and fillets (see p. 138), and it appeared that the technical process covers a wide continuous area and that it is applied in different ways by each cultural group. We have also seen that the characteristic triangular design with enclosed rectangle, often with spur lines along the base, is widely disseminated over the North American continent. We found that this form is common to the Pueblos, the Indians of the northwestern plateaus and of the plains, and that the fundamental pattern may be recognized in New England and Labrador. Patterns composed of lines, triangles and rectangles are characteristic of the art of the North American Indian.