Cranial ridge
The cranial ridges, also referred to as exo-cranial ridges or cranial plates are bony plates on the surface of the forehead on many humanoid species. Some species, such as Humans, Vulcans, and the ancient humanoids do not possess visible cranial ridges.

Klingon-Human hybrids generally inherited cranial ridges from their Klingon parent, although they were less pronounced. ()

In 2154, the Klingon augment virus, and the subsequent cure, caused many Klingons to lose their cranial ridges and become more like "Humans." This would be partially cured via cranial reconstruction. ()

During the 23rd century of the alternate reality, helmets issued to the Klingon Defense Force gave all warriors the appearance of cranial ridges. ()

As a child, B'Elanna Torres was often mocked and joked at because of her Klingon-inherited cranial ridges. She was referred to by Daniel Byrd as "Miss Turtlehead." () Partly because of this bullying, after she discovered she was pregnant, Torres attempted to resequence the DNA of her fetus in order to eliminate the genes that would manifest cranial ridges. However, she was convinced by her husband, Tom Paris, to abandon this effort. ()

The Cytherian encountered by the  in 2367 was fascinated by Worf's prominent cranial plate, among other things. ()

In 2370 of an alternate timeline, Alexander Rozhenko made a plaster cast of his forehead cranial ridges as a birthday gift to his father, Worf, who received it with pride. ()

When he de-evolved due to Barclay's Protomorphosis Syndrome, Worf's cranial plates thickened by 20%. ()

Death is immediate for a Klingon if the cranial exoskeleton is shattered at the tricipital lobe. ()

Ktarians have sharp exocranial ridges, which are also present in Ktarian-Human hybrids. If the mother is human, these ridges can cause a rare complication where they become lodged in the uterine wall, as was the case with Naomi Wildman's birth in 2372. ()

Species with cranial ridges 
 Only Klingons have been stated to have "cranial ridges." The following species have been observed to have ridge-like structures, indicating bone, underneath their foreheads.
 Abaddon's species
 Abdon's species
 Akaali
 Akritirian
 Algolian
 Allos' species
 Andoran
 Andorian
 Ankari
 Annari
 Antaran
 Antarian
 Antedian
 Antican
 Argrathi
 Arkarian
 Arkonian
 Axanar
 Axum's species
 B'omar
 Banea
 Barzan
 Benkaran
 Benthan
 Borothan
 Boslic
 Botha
 Brunali
 Caatati
 Caldonian
 Cardassian
 Chalnoth
 Chokuzan
 Cytherian
 Dala's species
 Daliwakan
 Dee'Ahn's species
 Denobulan
 Devore
 Dralian
 Dream Aliens
 Efrosian
 El-Adrel IV lifeform
 Elaysian
 Emi's species
 Entharan
 Eska
 Etanian
 Fallit Kot's species
 Fantome's species
 Farian
 Flaxian
 Garan
 Gosis' species
 Grazerite
 Haakonian
 Hanonian
 Hazari
 Hekaran
 Hirogen
 Idanian
 Ilari
 Illyrian
 Iyaaran
 J'naii
 Jarlath's species
 Jem'Hadar
 Kadi
 Kago's species
 Karemma
 Kazon
 Kesat
 Kesprytt
 Klingon
 Kobliad
 Kolaati
 Kolaran
 Kreetassan
 Kressari
 Krit's species
 Ktarian
 Ledosian
 Lethean
 Lokirrim
 Malcorian
 Malon
 Markalian
 Mintakan
 Miradorn
 Mislenite
 Mizarian
 Na'kuhl
 Napean
 Nara's species
 Nasari
 Nausicaan
 Nezu
 Night Alien
 Nuvian
 Nygean
 Osaarian
 Otrin's species
 Pakled
 Pandronian
 Parada
 Pelian
 Pendari
 Pomet's species
 Prah Mantoos' species
 Promellian
 Qomar
 R'Kaal
 Rakhari
 Rakosan
 Retellian
 Rigelian
 Romulan Northerners
 Rotciv
 Sakari
 Saowin's species
 Sarda's species
 Selay
 Sky Spirit
 Solanogen-based lifeform
 Solari
 Species 571
 Species 6339
 Species 8472
 Species 10026
 Swarm species
 Tak Tak
 Takaran
 Talarian
 Talaxian
 Talura's species
 Tamarian
 Tanugan
 Tarkalean
 Tarlac
 Tarquin's species
 Tash's species
 Telsian
 
 Tessic's species
 Tiburonian
 Tilonian
 Trabe
 Tret's species
 Triannon
 Turei
 Tygarian
 V'radian
 Vaadwaur
 Valerian
 Varn's species
 Vaskan
 Ventu
 Vhnori
 Vian
 Vidiian
 Viorsa's species
 Voth
 Wysanti
 Xindi-Arboreal
 Xindi-Primate
 Xindi-Reptilian
 Xyrillian
 Yost's species
 Yridian
 Zahl
 Zalkonian
 Zaranite
 Zolan's species

Appendices

See also 
 Nose ridge

Background information 
During Star Trek productions, some aliens were introduced without ridges, but ridges were added in later productions. Some aliens this happened to include:
 Romulans ( vs. )
 Klingons ( vs. )
 Andorians ( vs. )
 Tiburonians ( vs. )

In the final draft script of , a person off-screen who Charles Tucker III and Malcolm Reed notice in a Risan nightclub was scripted to be referred to as having cranial ridges, with Reed stating, "She's got lovely cranial ridges." However, the only comment made about this unseen individual in the final version of the episode is Tucker remarking, "I don't think 'she' is the right pronoun."
Bones