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The multiple bones of a bluefin tuna head


Skull of a bluefin tuna (Thunnus thynnus, Scombridae)

Despite the more than 200 bones in the head, bluefin tuna is not the acanthomorph with the most complex skull anatomy. The skull of the remoras (Echeneidae), with a dorsal fin transformed in a sucker and extending onto the head, or the asymmetrical skull of flatfish (pleuronectiformes), or the flattened skull of a monkfish (Lophius piscatorius, Lophiidae) are few examples of higly modified skulls. But, because of their size, the bones of the skull of a bluefin tuna are good tools to learn to identify bony structures.

The different ostéologic layers, from the most superficial bones to intern ones, are here exposed, as they appear during an osteologic dissection.

The colour of the legends refers to the origin of the :
in red : dermal bones,
in blue : enchondral bones,
in purple : bones of mixte origin (dermal and enchondral).


On all images, scale bar indicates 10 cm.


1èr layer : superficial dermal skeletonlocalisation du squelette superficiel dermique squelette superficiel dermique

Superficial dermal skeleton of a bluefin tuna (Thunnus thynnus), left laterale view (scale bar: 10cm).

Abbreviations

Nom français

English name

scl sclérotique sclerotic
la (io1) lacrymal (= infraorbital 1) lachrymal (= infraorbital 1)
c s io canal sensoriel infra-orbitaire infra-orbital sensory canal
io 2-6 infra-orbitaire ou infra-orbital (numérotés de 2 à 6) infra-orbital (numbered from 2 to 6)
exsc extrascapulaire extrascapular
art hyomd articulation avec l'hyomandibulaire hyomandibular articulation
op operculaire opercular
pop préoperculaire preopercular
sop sous-operculaire sub-opercular
iop interoperculaire interopercular

2nd layer: appendicular skeleton

Only the pectoral girdle is shown here. To examine the pelvic girdle, please have a look to the page dedicated to osteological systems.

localisation du squelette appendiculaire squelette appendiculaire

Squelette Appendicular skeleton of a bluefin tuna  (Thunnus thynnus), left lateral view (scale bar: 10cm).

Abbreviations

Nom français

English name

exsc extrascapulaire extrascapular
spcl supracleithrum supracleithrum
mtcl métacleithrum metacleithrum
lep lépidotriche lepidotriche
cl cleithrum cleithrum
rd radial radial
sc scapulaire scapula
co coracoïde coracoid

3rd layer: splanchnocranium (gill arches excepted)

localisation du splanchnocrâne splanchnocrâne
Splanchnocranium of a bluefin tuna (Thunnus thynnus), left lateral view (scale bar: 10cm).
 

Abbreviations

Nom français

English name

pmx prémaxillaire premaxilla
mx maxillaire maxilla
pal palatin palatine
d dentaire dentary
ang-art angulo-articulaire angulo-articular
c carré quadrate
ecpt ectoptérygoïde ectopterygoid
mtpt métaptérygoïde metapterygoid
entpt entoptérygoïde entopterygoid
hyomd hyomandibulaire hyomandibula
fc art n facette d'articulation avec le neurocrâne articulary facet with the neurocranium
fc art op facette d'articulation avec l'operculaire articulary facet with the opercular
sy symplectique symplectic
ephy épihyal epihyal
cthy cératohyal ceratohyal
r br rayon branchiostège gill ray
hphy hypohyal hypohyal
bhy basihyal basihyal

4rd layer: gill arches

localisation des arcs branchiaux arcs branchiaux
Gill arches of a bluefin tuna (Thunnus thynnus), left lateral view (scale bar: 10cm).

Abbreviations

Nom français

English nam

bhy basihyal basihyal
u urohyal urohyal
bbr 1-3 basibranchial (numérotés de 1 à 3) basibranchial (numbered from 1 to 3)
hpbr hypobranchial hypobranchial
crbr cératobranchial ceratobranchial
crbr 5 cératobranchial 5 ceratobranchial 5
epbr épibranchial epibranchial
phbr pharyngobranchial pharyngobranchial
arc br arc branchial branchial arc
arc br 2 arc branchial 2 branchial arc 2
o d d os dermique dentigère dentigerous dermic bone

5. Neurocranium

The neurocranium is the most intern structure of the skull. It surrounds and protects the encephalon (= "brain"). To study its organisatoon, please consult the page neurocranium.