The evolution of the morphology and structure of the mandible and

Rom J Leg Med [19] 111-114 [2011]
DOI: 10.4323/rjlm.2011.111
© 2011 Romanian Society of Legal Medicine The evolution of the morphology and structure of the mandible and
temporo - mandibulary joint. Medico legal identification criteria
Giorgică Lupu1, Daniel Popescu1*, Victor Pănuş1, Gabriela Popescu1, Luca Stan-Sion2, George Petre2
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Abstract: The study of the configuration and composition of the mandible in vertebrates reveals intersting aspects
regarding the relation between its structure and function; as we move on phylogenetic scale we find that the mandible changes
its composition and its configuration, as a way of adaptation to the underwater and then earth life, to the type of food and to
language development, in terms of sensory component, hearing, motor and verbal. Paradoxically, we find that the evolution of
the complexity of structure (but not the shape) and function of the mandible is inversed in the way that if at the bottom of the
vertebrates scale (at fish) the lower jaw has a complex configuration, from more components, at the top (at human being) the
lawer jaw keeps one component but it executes the finenst and more complex movements in the temporomandibulary joint.
Key Words: lower jaw, phylogenesis, vertebrates, language
S
tarting with the arguments of the “Summary Theory” under which each organism goes through all
stages of phylogenesis, we analyzed the evolution of the mandible in all vertebrates and cordatas
species: fish, amphibians, reptiles, birds and mammals; we found out in this way the evolution of the bone
components which formed the mandible or the inferior jaw of the inferiors vertebrates (dental, angular,
articular, coronoid ans quadrant bones) to mandible and the temporomandibulary joint of mammals and
we also underlined the structure and configuration changes of the temporomandibulary joint in rodents
mammals, herbivorous and carnivoressi the qualitative jump in human being thanks to articulated language.
Purpose
Knowing the complexity and the importance of the temporomandibulary joint in humans, the
purpose of our study was to underline the origins of the bone components of this joint and its evolutiont
in vertebrates, to human, so we can demonstrate that all structure and configuration modifications have
happened following the adaptation to the type of food and mastication and finally, to the articulated language.
Material and method
The macro and mesoscopic were made with the equipment of the editorial staff of The Department
of Anatomy of The Faculty of Medicine of UMF “Carol Davila”, Bucharest, and with the support of the
teachers and researchers from The Faculty of Biology from The University of Bucharest, The Faculty of
Veterinary Medicine within The University of Agricultural Sciences and Veterinary Medicine Bucharest
and The National Museum of Natural History “Grigore Antipa”, Bucharest.
1) Anatomy department of UMF Carol Davila, Bucharest
* Corresponding author: Associate Professor Daniel Popescu, Nr.8, Eroii Sanitari Blvd, Sector 5, Bucharest,
Romania, e-mail: [email protected]
2) Student at UMF Carol Davila, Bucharest
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We used anatomical parts (skulls) from different species of vertebrates and fetal skulls of different
ages obtained through our own methods; these were analyzed and photographed and the images were
digitally processed in order to obtain the most suggestive details.
Results
Discutions. At the bottom of
the evolution scale of vertebrates
are the fish; their mandible has a
complex composition, it is formed
from more components : dental,
angular, articular and quadrant.
The quadrant bone aerticulates
with hiomandibular bone from the
bottom of the skull.
Fig. 1. Fish Mandible
In frog the hiomandibular bone
is released from the joint with the jaws, it is
transforming in columella and migrates in
the middle ear, which appears for the first
time in vertebrates, as they pass from the
aquatic life to terrestrial environment (due
to the different way of sound propagation of
sound in the two environments). The articular
bone articulates with the quadrant so that the
mandible articulates with the skull through
the quadrantarticulara articulation. The
dental bone shows in front a cartilaginous
region “pars mentalis”, the zone where the
tongue is fixed in amphibians.
Fig. 2. The mandible in amphibians
The snake, from the reptiles class, has the
mandible branches flexible articulated through
the quadrantoarticular joint; they can be moved
independent through the elastic ligament which
links the two halves of the mandible.
Fig. 3. The mandible in snake
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In birds – the pieces from which the mandible
is made of merge early and they are protected by a horny
coating which enters in the composition of the beak. The
external ear plots through an external auditory meatus
completed with a rudimentary auricle.
Fig. 4. Mandible in birds
Fig. 5. The evolution of the structure and configuration of the mandible from birds to mammals.
In mammals, with the exception af the dental bone which will forme the mandible entirely, the rest of
the components will penetrate in the bottom of the skull as follows:
-the angular bone turns in the tympanic part of the temporal bone
-the erticular bone turns in malleus
-the quadrant bone turns in inchus
-the ear leadder will be derivative of the second gill arch, respectively the hiomandibular bone from
the fish.
In humans the process of evolution and
transformation of the mandible is visible in fetal
skulls; yet from the IV-th month the configuration of
the middle ear with the bones chain is sketched, and
the tympanic part of the temporal bone, derivative
from the angular bone, has the shape of a incomplete
bony ring which partially ensure the insertion of the
tympanic membrane.
Fig. 6. The final stage of phylogenetic evolution of the mandible
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The evolution of the morphology and structure of the mandible and temporo - mandibulary joint
Acknowledgements
The configuration of mandible and temporomandibulary joint may be an identification criteria for
medico legal cases. Also, the evolution of middle ear is a landmark for age appreciation of human
fetal skull.
The mandible, in its phylogenetic evolution to vertebrates simplify its composition, in mammals and
in humans it is formed only from the dental bone of the inferior vertebrates (fish, reptiles).
The modification of the mandible shape it is initially made as an adaptation to the main acts of import
of the matter from the external environment (breathing, mastication), and as we move foward on the
vertebrates` scale, aqs a way of adaptation to the type of food (in mammals the shape is different to
rodents, herbivorous and carnivores).
In the same time with this way of adaptation to one of the essential instincts of species conservation,
the nutrition, the mandible evolves with the purpose of establish a relation or communication between
the individuals; in this way, part of the initial components of the composition of the mandible to
inferior vertebrates will participate to building the acoustic analyzer (the hammer and the incus
from the middle ear or the tympanic part of the temporal bone from the constitution of the external
auditory meatus).
Spectacular changes of configuration take place in the mammals mandible, in relation with the
most evolved form of communication, phonation or the speech; in this way the configuration of the
mandible` head and the structure of the first temporobandibular joint will be perfectly adapted to the
type of carnivore mastication (omnivorous) but to articulated language.
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