Head shape and cranial protuberances

The head of a chameleon varies a great deal, depending on the species and genus.

True horns:

True horns consist of a core of bone and are covered by a thin keratin shell that is often covered by rings.
The best known species with true horns is undoubtedly Trioceros jacksonii, but there are many other species that have evolved in this way, however only for those species within the genus Trioceros.

False horns:

False horns vary in shape, but like true horns, they have a core of bone, but in this case they are covered by larger tubercular or plate-like scales.
The most well-known species with false horns is probably, Kinyongia multituberculata, which is known for its long ‘nose’, but numerous other species have also developed false horns.

False horns are found in the genera Brookesia, Calumma, Furcifer, Kinyongia, Palleon and Trioceros

Soft protuberance:

This type of protuberance is soft, slightly pliable and is often covered with granular scales. 
It is mostly seen in Rhampholeon and Calumma species.

The exception:

Kinyongia oxyrhina and Kinyongia tenuis are somewhat intermediate, since the tip of the nose is soft and pliable, but the proximal part is made of  bone.

Source:
Books:
Chamaeleonidae. By J.J Klaver & W.Böhme.
Chameleons Nature´s hidden jewles. By Petr Necas.
Chameleons of Africa. By Colin Tilbury.
Stump-tailed chameleons Miniature dragons of the rainforest. By Petr Necas.
The Biology of Chameleons. By Krystal A. Tolley & Anthony Herrel.

Publications:
ANANJEVA. N.B- 1991- the skin sense organs of some Iguanian lizards.

Picture copyright:
Achim Lerner
Alex Laube.
Bobby Bok.
Chameleondatabase.com
Christopher V. Anderson. Chamaeleonidae.com
Cody Pope.
Drew Weber.
Giovanni Caddeo.
Guido Coza.
Guy Kremer.
Jan Stipala.
Lynne.
Marc Vaillant.
Marco Von der Osten.
Martin Knauf.
Mary Lovein.
Mike Fisher.
Olaf Pronk.
Petr Necas.
Paul Bertner. Flickr.
Roy J. Hinde.
Stephen Woodham.

Edited by Paul Freed.