Plastron

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Plastron

The plastron is the nearly flat part of the shell structure of a turtle

Turtle

Turtles are reptiles of the Order Testudines , most of whose body is shielded by a special bone or cartilage animal shell developed from their ribs....
or tortoise

Tortoise

Carapace

A carapace is a Dorsum section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids as well as vertebrates such as chelonians, order Testudines, turtles and tortoises....
; with an external layer of horny material divided into plates called scute

Scute

A scute or scutum is a chitinous, or bony external plate or scale, as on the shell of a turtle, the skin of crocodiles, or the feet of some birds....
s and an underlying layer of interlocking bones.

In certain families there is a hinge between the pectoral

Pectoral

Pectoral, from the Latin pectoralis , "pertaining to the breast/chest", can refer to:* Pectoral cross, a cross worn on the chest* a decorative, usually jeweled version of a gorget...
and abdominal scutes allowing the turtle to almost completely enclose itself.

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Encyclopedia

The plastron is the nearly flat part of the shell structure of a turtle

Turtle

Turtles are reptiles of the Order Testudines , most of whose body is shielded by a special bone or cartilage animal shell developed from their ribs....
or tortoise

Tortoise

Carapace

Scute

Pectoral

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring....
the sex of a testudine can be told by whether the plastron is concave, male or convex, female. This is because of the mating position.

The plastral scutes join along a central seam down the middle of the plastron. The relative lengths of the seam segments can be used to help identify a species of turtle

Turtle

Turtles are reptiles of the Order Testudines , most of whose body is shielded by a special bone or cartilage animal shell developed from their ribs....
or tortoise

Tortoise

Tortoises or land turtles are land-dwelling reptiles of the family of Testudinidae, order Turtle. Like their marine cousins, the sea turtles, tortoises are shielded from predators by a shell....
. There are six laterally symmetric pairs of scutes on the plastron: gular, humeral, pectoral, abdominal, femoral, and anal (going from the head to the tail down the seam).

Indicating that the abdominal and gular scute seams are approximately the same length and the femoral and pectoral seams are approximately the same length. Comparison of the plastral formulas provides distinction between the two species.

Turtle plastrons were used by the ancient Chinese in a type of divination

Divination

Divination is the attempt to gain insight into a question or situation by way of a standardized process or ritual. Diviners ascertain their interpretations of how a querent should proceed by reading signs, events, or omens, or through alleged contact with a supernatural agency....
called plastromancy

Plastromancy

Plastromancy is a form of pyromancy divination using the plastron, or undershell of a turtle. It was mainly used in ancient China, especially the Shang dynasty....
. See also oracle bone

Oracle bone

Oracle bones are pieces of bone or animal shell that were heated and cracked, using a bronze pin, during divination, chiefly during the late Shang Dynasty, and then typically inscribed with a record of the reflexes in what is known as oracle bone script....
s.

Other Meanings

Plastron is a name that has also been given to various coverings or structures on the ventral (belly) side of some creatures, people or objects.

"Plastron" is the name of a broad piece of material placed on the chest of certain military uniform
Military uniform

Military uniforms comprises standardised dress worn by members of the armed forces and Paramilitary of various nations. Military dress and military styles have gone through great changes over the centuries from colourful and elaborate to extremely utilitarian....
s and held in place by two rows of buttons. The plastron was a popular feature of military dress during the period 1800-1914, when it was commonly worn by lancer
Lancer

A lancer was a type of cavalryman who fought with a lance. Lances were used in mounted warfare by the Assyrians as early as 700BC and subsequently by Greek, Macedonian, Persian, Gallic and Roman horsemen" The weapon was widely used in Asia and Europe during the Middle Ages and the Renaissance by armoured cavalry before being adopted by light...
and uhlan
Uhlan

Uhlans were Polish light cavalry armed with lances, sabres and pistols. The title was later used by lancer regiments in the Prussian and Austro-Hungarian Empire armies....
regiments in various European armies. It was also worn by light dragoon regiments in the British Army and by infantry and artillery units in the Imperial Russian Army. Plastrons were usually in contrasting colours to those of the tunics or coats that they were attached to.
The name of the bulge on an aircraft, such as the Airbus A340
Airbus A340

The Airbus A340 is a long-range four-engined wide-body commercial passenger airliner manufactured by Airbus, a subsidiary of EADS. It seats between 261 and 380 passengers, and has a range between 6,700 and 9,000 nautical miles....
, under the fuselage
Fuselage

The fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a hardpoint attached to the fuselage which in turn is used as a floating Hull ....
between the wings that is used to correct airflow around the engine pylon
Hardpoint

A hardpoint is any part of an airframe designed to carry an external load. This technical description includes mountings for podded engines, but most commonly the term is used, as with weapon station, to refer to a point on the wings of military aircraft where external stores such as missiles, bombs, countermeasures, gun pods, or drop...
s. On many aircraft, this bulge also helps house the main undercarriage
Undercarriage

In aviation, the undercarriage or landing gear is the structure that supports an aircraft on the ground and allows it to taxiing....
when retracted.
A "plastron" is also a thin permanent layer of air around the body of some aquatic insects, held in place by hydrophobic hairs, and acting as a physical gill
Gill

A gill is an anatomical structure found in many aquatic ecosystem organisms. It is a respiration organ whose function is the extraction of oxygen from water and the excretion of carbon dioxide....
.
"Plastron" is also the name of a one-arm, half-jacket used in the sport of fencing.
It is also the name of a chest guard, used in the archery
Archery

Archery is the art, practice or skill of shooting with Bow and arrow. Archery has historically been used in hunting and combat and has become a precision sport....
, preventing the bowstring from being obstructed by the archer's body or clothing as it is released.