Jaw Suspension in Vertebrates
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Jaw suspension means attachment of
Jaw suspension means attachment of the lower jaw with the upper jaw.
There are different ways in which these attachments are attained depending upon the
modifications in visceral arches in vertebrates.
1 Autodiastylic:
Upper jaw is attached with the skull and lower jaw is directly attached to the upper jaw.
The second arch is a branchial arch and does not take part in jaw suspension.
2 Amphistylic: In primitive elasmobranchs there is no modification of visceral arches and they are made of cartilage. Pterygoqadrate makes the upper jaw and meckel’s cartilage makes lower jaw and they are highly flexible. Hyoid arch is also unchanged. Lower jaw is attached to both pterygoqadrate and hyoid arch and hence it is called amphistylic.
3 Hyostylic: In modern sharks, lower jaw is attached to pterygoquadrate which is in turn attached to
hyomandibular cartilage of the 2nd arch. It is the hyoid arch which braces the jaw by ligament
attachment and hence it is called hyostylic.
4 Autostylic: Pterygoquadrate is modified to form epipterygoid and quadrate, the latter braces the lower jaw with the skull. Hyomandibular of the second arch transforms into columella bone of the middle ear cavity and hence not available for jaw suspension.
i) Monimostylic: This type of suspension is a modification of autosystylic suspension in which quadrate
is immovable and not flexible as in amphibia and many reptiles. Hyomandibular is modified as
columella bone of the middle ear cavity.
ii)Holostylic: This type is found in lung fishes and Holocephali. Upper jaw is fused with the skull and
the lower jaw is attached directly with it. Hyoid arch does not participate in jaw suspension and is a
typical branchial arch. There is no columella bone.
iii)Streptostylic: This types of skull is found in snakes, lizard and birds. Quadrate bone is movable and flexible at both end making the jaw highly flexible.
5 Craniostylic: Found in mammals, in this type of jaw suspension, pterygoquadrate is transformed into alisphenoid and incus, while meckel’s cartilage is changed into malleus and not available for jaw
suspension. Lower jaw is directly attached to the skull bone called squamosal. Monotremes also
possess this type of jaw suspension.
There are different ways in which these attachments are attained depending upon the
modifications in visceral arches in vertebrates.
1 Autodiastylic:
Upper jaw is attached with the skull and lower jaw is directly attached to the upper jaw.
The second arch is a branchial arch and does not take part in jaw suspension.
2 Amphistylic: In primitive elasmobranchs there is no modification of visceral arches and they are made of cartilage. Pterygoqadrate makes the upper jaw and meckel’s cartilage makes lower jaw and they are highly flexible. Hyoid arch is also unchanged. Lower jaw is attached to both pterygoqadrate and hyoid arch and hence it is called amphistylic.
3 Hyostylic: In modern sharks, lower jaw is attached to pterygoquadrate which is in turn attached to
hyomandibular cartilage of the 2nd arch. It is the hyoid arch which braces the jaw by ligament
attachment and hence it is called hyostylic.
4 Autostylic: Pterygoquadrate is modified to form epipterygoid and quadrate, the latter braces the lower jaw with the skull. Hyomandibular of the second arch transforms into columella bone of the middle ear cavity and hence not available for jaw suspension.
i) Monimostylic: This type of suspension is a modification of autosystylic suspension in which quadrate
is immovable and not flexible as in amphibia and many reptiles. Hyomandibular is modified as
columella bone of the middle ear cavity.
ii)Holostylic: This type is found in lung fishes and Holocephali. Upper jaw is fused with the skull and
the lower jaw is attached directly with it. Hyoid arch does not participate in jaw suspension and is a
typical branchial arch. There is no columella bone.
iii)Streptostylic: This types of skull is found in snakes, lizard and birds. Quadrate bone is movable and flexible at both end making the jaw highly flexible.
5 Craniostylic: Found in mammals, in this type of jaw suspension, pterygoquadrate is transformed into alisphenoid and incus, while meckel’s cartilage is changed into malleus and not available for jaw
suspension. Lower jaw is directly attached to the skull bone called squamosal. Monotremes also
possess this type of jaw suspension.
4 سال پیش
در تاریخ 1399/07/30 منتشر شده
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