Simplify the following text for a Grade 11 native English-speaking person.
Original: Porcupines ' quills , or spines , take on various forms , depending on the species , but all are modified hairs coated with thick plates of keratin , and they are embedded in the skin musculature .
Simplified: The animal 's quills or spines take on many forms , depending on the type , but all are hairs coated with thick plates of keratin , and they are in the skin musculature .