The objective of this article is to explore the topic of Hebrew illuminated manuscripts in the region of present-day Germany in the 13th and 14th centuries. A part of them comprise a relatively closed group which is characterized by the special depiction of the heads of figures: various modifications or deformations of faces of predominantly Jewish characters. A typical substitution is the use of an animal or birdlike face instead of the human one, of a face in which all substantial traces, such as eyes, mouth or nose, are missing, or the whole head is covered with a crown or hat, or the head is depicted from the rear. -- The topic of deformations, alterations and substitutions of human faces in Hebrew illuminated manuscripts is analyzed and illustrated in numerous examples. The possible ancient origin of figures with animal or bird-like heads is discussed, as well as the standpoint of medieval Jewish scholars on the biblical prohibition of images, especially in relation to the issue of deformations and substitutions of faces in Hebrew illuminated manuscripts. The final part of the paper deals with modern interpretations of the whole subject (Ameisenowa, Jaffé, Strauss, Narkiss, Mellinkoff).