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Suture (anatomical)
Encyclopedia
In anatomy
, a suture is a fairly rigid joint between two or more hard elements of an animal, with or without significant overlap of the elements.
Sutures are found in the skeletons or exoskeletons of a wide range of animals, in both invertebrate
s and vertebrate
s, from the Cambrian
period to the present day. Sutures were and are formed by several different methods, and they exist between hard parts that are made from several different materials.
, in which the main rigid ingredient is calcium phosphate
.
The crania (brain cases) of most vertebrates consist of sets of bony plates held together by cranial sutures
. These sutures are held together mainly by Sharpey's fibers which grow from each bone into the adjoining one.
In the type of crurotarsal
ankle which is found in crocodilians and some other archosaurs, the astragalus
is fixed to the tibia
by a suture, and the joint bends around a peg on the astragalus, which fits into a socket in the calcaneum.
(the main constituent of limestone
and chalk
), and of conchiolin
, a protein. For more information, see Mollusc shell
.
In cephalopod
mollusks which have external shells (e.g. Nautilus
, ammonites), the shell is divided into compartments by septa
("partitions").
The septa are joined to the external shell by sutures formed by "repeated invagination" (they interlock like pieces of a jigsaw puzzle
). The sutures are visible from the outside and often form complex and elaborate patterns.
Nearly all snail shells (except for the shells of limpets) can be visualized as a tube of increasing diameter, closed at the small end, and spirally wrapped around a central axis. For more information, see Gastropod shell
.
Each complete rotation of this spirally-arranged tube is called a whorl
. The whorls of a snail shell usually overlap one another, forming a spire
. Where the whorls overlap, there is usually a clear (if narrow) indentation. This indentation forms a visible line, which is continuous and reaches from the apex
of the shell to the aperture
; this line is the suture.
Details of the suture are often useful in discriminating one species from another, for example, sometimes the suture is channeled.
The suture also provides a sort of geographic marker from which one can refer to the positioning of patterning or sculpture
, where that is relevant: for example some species have a darker or lighter subsutural band on the shell.
When an angulation of the whorls occurs, the space between it and the suture above it (i.e. the abaxial edge of the sutural ramp) constitutes the area known as the "shoulder" of the shell. The shoulder angle may be simple or keeled, an may sometimes have nodes or spines
Sutures in the carapaces of trilobite
A trilobite's carapace consisted of calcite
and calcium phosphate
deposited on a lattice (framework) of chitin
(a complex sugar).
The trilobite body is divided into three major sections: a cephalon (head section) with eyes, mouthparts and sensory organs such as antennae; a thorax of multiple segments which are similar to each other; and a pygidium, or tail section.
In many species the cephalon had sutures running from back to front round the outside edges of the eyes. These sutures divided the cephalon into 3 pieces.
The sutures in trilobites' cephalons were unusual because it seems their main function was to create weaknesses which made it easy for this part of the carapace
("armor") to split when the animal needed to molt
.
Anatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...
, a suture is a fairly rigid joint between two or more hard elements of an animal, with or without significant overlap of the elements.
Sutures are found in the skeletons or exoskeletons of a wide range of animals, in both invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s and vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s, from the Cambrian
Cambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
period to the present day. Sutures were and are formed by several different methods, and they exist between hard parts that are made from several different materials.
Vertebrate skeletons
These skeletons are made of boneBone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
, in which the main rigid ingredient is calcium phosphate
Calcium phosphate
Calcium phosphate is the name given to a family of minerals containing calcium ions together with orthophosphates , metaphosphates or pyrophosphates and occasionally hydrogen or hydroxide ions ....
.
Cranial sutures
Cranial sutures
*Surgical suture, to describe stitches and other techniques for holding tissues together.* Geology, to describe a certain type of boundary between layers of rock....
. These sutures are held together mainly by Sharpey's fibers which grow from each bone into the adjoining one.
Sutures in the ankles of land vertebrates
Crurotarsal
A crurotarsal joint is one that’s situated between the bones of crus, i.e. shin and the proximal tarsal bones, i.e. astragalus and calcaneum....
ankle which is found in crocodilians and some other archosaurs, the astragalus
Talus bone
-External links:* *...
is fixed to the tibia
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
by a suture, and the joint bends around a peg on the astragalus, which fits into a socket in the calcaneum.
In molluscs
The shells of most molluscs are made of calcium carbonateCalcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
(the main constituent of limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
and chalk
Chalk
Chalk is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates shed from micro-organisms called coccolithophores....
), and of conchiolin
Conchiolin
Conchiolin and perlucin are complex proteins which are secreted by a mollusc's outer epithelium ....
, a protein. For more information, see Mollusc shell
Mollusc shell
The mollusc shell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which includes snails, clams, tusk shells, and several other classes...
.
Sutures in the shells of cephalopods
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
mollusks which have external shells (e.g. Nautilus
Nautilus
Nautilus is the common name of marine creatures of cephalopod family Nautilidae, the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina. It comprises six living species in two genera, the type of which is the genus Nautilus...
, ammonites), the shell is divided into compartments by septa
Septum
In anatomy, a septum is a wall, dividing a cavity or structure into smaller ones.-In human anatomy:...
("partitions").
The septa are joined to the external shell by sutures formed by "repeated invagination" (they interlock like pieces of a jigsaw puzzle
Jigsaw puzzle
A jigsaw puzzle is a tiling puzzle that requires the assembly of numerous small, often oddly shaped, interlocking and tessellating pieces.Each piece usually has a small part of a picture on it; when complete, a jigsaw puzzle produces a complete picture...
). The sutures are visible from the outside and often form complex and elaborate patterns.
The suture in the shells of gastropods
Gastropod shell
The gastropod shell is a shell which is part of the body of a gastropod or snail, one kind of mollusc. The gastropod shell is an external skeleton or exoskeleton, which serves not only for muscle attachment, but also for protection from predators and from mechanical damage...
.
Each complete rotation of this spirally-arranged tube is called a whorl
Whorl (mollusc)
A whorl is a single, complete 360° revolution or turn in the spiral growth of a mollusc shell. A spiral configuration of the shell is found in of numerous gastropods, but it is also found in shelled cephalopods including Nautilus, Spirula and the large extinct subclass of cephalopods known as the...
. The whorls of a snail shell usually overlap one another, forming a spire
Spire (mollusc)
A spire is a descriptive term for part of the coiled shell of mollusks. The word is a convenient aid in describing shells, but it does not refer to a very precise part of shell anatomy: the spire consists of all of the whorls except for the body whorl...
. Where the whorls overlap, there is usually a clear (if narrow) indentation. This indentation forms a visible line, which is continuous and reaches from the apex
Apex (mollusc)
Apex is an anatomical term for the tip of the mollusc shell of a gastropod, scaphopod, or cephalopod mollusc.-Gastropods:The word "apex" is most often used to mean the tip of the spire of the shell of a gastropod...
of the shell to the aperture
Aperture (mollusc)
The aperture is an opening in certain kinds of mollusc shells: it is the main opening of the shell, where part of the body of the animal emerges for locomotion, feeding, etc....
; this line is the suture.
Details of the suture are often useful in discriminating one species from another, for example, sometimes the suture is channeled.
The suture also provides a sort of geographic marker from which one can refer to the positioning of patterning or sculpture
Sculpture (mollusc)
The sculpture of a mollusc shell is the three-dimensional ornamentation on the outer surface, as distinct from the basic shape of the shell itself or colouration. Sculpture may be concave as well as convex. Sometimes it has microscopic detail. Sculpture refers to the calcareous outer layer, not the...
, where that is relevant: for example some species have a darker or lighter subsutural band on the shell.
When an angulation of the whorls occurs, the space between it and the suture above it (i.e. the abaxial edge of the sutural ramp) constitutes the area known as the "shoulder" of the shell. The shoulder angle may be simple or keeled, an may sometimes have nodes or spines
Sutures in the carapaces of trilobiteTrilobiteTrilobites are a well-known fossil group of extinct marine arthropods that form the class Trilobita. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period , and they flourished throughout the lower Paleozoic era before...
s
Calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...
and calcium phosphate
Calcium phosphate
Calcium phosphate is the name given to a family of minerals containing calcium ions together with orthophosphates , metaphosphates or pyrophosphates and occasionally hydrogen or hydroxide ions ....
deposited on a lattice (framework) of chitin
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...
(a complex sugar).
The trilobite body is divided into three major sections: a cephalon (head section) with eyes, mouthparts and sensory organs such as antennae; a thorax of multiple segments which are similar to each other; and a pygidium, or tail section.
In many species the cephalon had sutures running from back to front round the outside edges of the eyes. These sutures divided the cephalon into 3 pieces.
The sutures in trilobites' cephalons were unusual because it seems their main function was to create weaknesses which made it easy for this part of the carapace
Carapace
A carapace is a dorsal 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 turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
("armor") to split when the animal needed to molt
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
.