The line is missing commas. It should read, "Witches' mummy, maw and gulf..." (Macbeth, 4.1.24). The line references the ingredients that the witches are adding to the pot in which they are making a rather gruesome potion for Macbeth. The "mummy," refers to mummia, an ingredient like glue used to preserve mummies. "Maw" is an opening through which food is taken. Here it refers to the opening of the stomach, "gulf." It is thought that Shakespeare created these horrible mixtures as a caricature of Scottish cooking, particularly the delicacy, haggis. Haggis is a sheep or goat stomach stuffed with oatmeal and organ meats and then boiled.
This line appears in Act IV, scene 1 of Macbeth, when the witches are concocting another brew. Each witch is naming ingredients for the brew as she throws them in, and in this line the Third Witch is putting in dust scraped from a witch's mummy and the mouth (maw) and throat (gulf) of a ravenous (ravin'd) shark.