These ISOs are often called a number of different names, primarily because their exact function still hasn't been conclusively determined. The image above shows the head of an alligator with an enlarged view of the sensory pits on the outer edge of the lower jaw. There are none elsewhere on the animal. Distribution varies between species, and this is possibly related to their function.
Some scales possess three or four ISOs.
Except on the head, ISOs are normally positioned around the outer edge of a scale, and are visible as a pigmented spot. Function and structure of ISOs varies depending on their position around the body. Those around the jaws are mechanoreceptors which can detect pressure changes. Almost certainly, these sense organs are used when the crocodile is underwater to sense the proximity of prey items. A fish swimming past the head of an alligator, for example, will fire the sense organs as pressure waves from its movement through water impinge upon the ISOs.