For example, male lions have a collar of long, hard outline hair that grows continuously and extends to the shoulders and forms a mane on the back of the neck. Bristles function as visual signals that augment facial expressions (e.g., lions) or body postures (e.g., horses). Spines The guard hairs are sometimes modified to form defensive spines. Spines are the stiff, enlarged guard hairs that exhibit definitive growth and form the protective quills of echidnas, hedgehogs and especially porcupines. In porcupines, the cuticular scales are elongate and form barbs that make it difficult to remove imbedded spines. References Mammal anatomy