Leech, commonly known as leech, has three jaws in the mouth, one on the back and the other on the side. There are horny longitudinal ridges on the jaws, and each jaw has a row of fine teeth. For example, when leeches suck blood, they suck the host's skin tightly with the front sucker, and then cut a Y-shaped wound from the upper teeth of the lower jaw to suck blood. While sucking blood, the pharyngeal gland (.