Endocranium
Encyclopedia
For internal cast of the cranium, see Endocast
.
The endocranium in comparative anatomy
is a part of the skull base in vertebrates and represent the basal, inner part of the cranium. The term is also applied to the outer layer of the dura mater
in human anatomy
.
. The floor of the endocranium has several paired openings for the cranial nerves
, and the anterior margin holds a spongy construction, allowing for the external nasal nerve
s to pass through. All bones of the structure derive from the cranial neural crest
during fetal development
.
s, the endocranium forms during fetal development
as a cartilaginous neurocranium, that ossifies from several centers. Several of these bones merge, and in the adult, the endocranium is composed of only five bony elements (from front to back):
s is much reduced size and number of bones compared to the condition in the ancestral land vertebrates
, though the occipital bone
occur as several bony elements in several mammal groups. The occipital bone is also found as several bony elements in birds and reptiles, while the skull of modern amphibian
s is generally reduced with a simplified endocranium. The skull of early labyrinthodonts
were rather complex, and contained in addition to the bones mentioned above several small cartilagious components that are fused to temporal and occipital bones in mammals:
of the skull is more loose in the lower vertebrates
. In Agnathans and Chondrichthyes
, the skull lacks the skull roof
dermal elements, their whole cranium being composed of the endocranium, properly called a chondrocranium
. In most Osteichthyes
, the skull is only loosely joined, and the endocranial elements do not form a unit with the skull roof.
makes on the inside of the neurocranium (braincase), providing a replica of the brain with most of the details of its outer surface. Endocasts can also form naturally, when sediments fill the empty skull
, after which the skull is destroyed and the cast fossil
ized. Scientists are increasingly utilizing computerized tomography scanning technology to create digital endocasts without damaging valuable specimens. This gives a 3D representation of the brain. Brain size and complexity can then be determined.
Endocasts were used for looking at the brains of Homo sapiens to find hemispheric specialization.
Endocast
An endocast is the internal cast of a hollow object, often specifically used for an endocasts of the cranial vault. Endocasts can be man-made for examining the properties of a hollow, inaccessible space, or occur naturally through fossilisation....
.
The endocranium in comparative anatomy
Comparative anatomy
Comparative anatomy is the study of similarities and differences in the anatomy of organisms. It is closely related to evolutionary biology and phylogeny .-Description:...
is a part of the skull base in vertebrates and represent the basal, inner part of the cranium. The term is also applied to the outer layer of the dura mater
Dura mater
The dura mater , or dura, is the outermost of the three layers of the meninges surrounding the brain and spinal cord. It is derived from Mesoderm. The other two meningeal layers are the pia mater and the arachnoid mater. The dura surrounds the brain and the spinal cord and is responsible for...
in human anatomy
Human anatomy
Human anatomy is primarily the scientific study of the morphology of the human body. Anatomy is subdivided into gross anatomy and microscopic anatomy. Gross anatomy is the study of anatomical structures that can be seen by the naked eye...
.
Basic structure
Structurally, the endocranium consists of a boxlike shape open at the top. The posterior margin exhibit the foramen magnum, an opening for the spinal cordSpinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
. The floor of the endocranium has several paired openings for the cranial nerves
Cranial nerves
Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of cranial nerves...
, and the anterior margin holds a spongy construction, allowing for the external nasal nerve
External nasal nerve
The external nasal branches are terminal branches of the anterior ethmoidal nerves , and provide sensory innervation to the skin of the side of the nose and of the septum mobile nasi....
s to pass through. All bones of the structure derive from the cranial neural crest
Cranial neural crest
The cranial neural crest is a form of neural crest.The cranial neural crest arises in the anterior and populates the face and the pharyngeal arches giving rise to bones, cartilage, nerves and connective tissue...
during fetal development
Fetal development
Prenatal or antenatal development is the process in which a human embryo or fetus gestates during pregnancy, from fertilization until birth. Often, the terms fetal development, foetal development, or embryology are used in a similar sense.After fertilization the embryogenesis starts...
.
Endocranial elements in humans
In humans and other primatePrimate
A primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...
s, the endocranium forms during fetal development
Fetal development
Prenatal or antenatal development is the process in which a human embryo or fetus gestates during pregnancy, from fertilization until birth. Often, the terms fetal development, foetal development, or embryology are used in a similar sense.After fertilization the embryogenesis starts...
as a cartilaginous neurocranium, that ossifies from several centers. Several of these bones merge, and in the adult, the endocranium is composed of only five bony elements (from front to back):
- The Ethmoid bone, lying behind the nose.
- The Sphenoid boneSphenoid boneThe sphenoid bone is an unpaired bone situated at the base of the skull in front of the temporal bone and basilar part of the occipital bone.The sphenoid bone is one of the seven bones that articulate to form the orbit...
, underlying the forward portion of the brain - Paired petrous part of the temporal bones, containing the inner earInner earThe inner ear is the innermost part of the vertebrate ear. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:...
structures - The Occipital boneOccipital boneThe occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoidal in shape and curved on itself...
, surrounding the foramen magnum
Endocranial components in other tetrapods
The endocranium in mammalMammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s is much reduced size and number of bones compared to the condition in the ancestral land vertebrates
Tetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
, though the occipital bone
Occipital bone
The occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoidal in shape and curved on itself...
occur as several bony elements in several mammal groups. The occipital bone is also found as several bony elements in birds and reptiles, while the skull of modern amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s is generally reduced with a simplified endocranium. The skull of early labyrinthodonts
Labyrinthodontia
Labyrinthodontia is an older term for any member of the extinct subclass of amphibians, which constituted some of the dominant animals of Late Paleozoic and Early Mesozoic times . The group is ancestral to all extant landliving vertebrates, and as such constitutes an evolutionary grade rather...
were rather complex, and contained in addition to the bones mentioned above several small cartilagious components that are fused to temporal and occipital bones in mammals:
- Paired prootic and opisthotic bones above each fenestra ovalis, fused to the petrous part of the temporal bones in mammals.
- Paired exoccipital bones medially and a single basioccipital bone below the foramen magnum, part of the occipital bone in mammals.
The endocranium in fishes
While the endocranium is an integral part of the skull in mammals, birds and reptiles, its connection to the roofing partsSkull roof
The skull roof , or the roofing bones of the skull are a set of bones covering the brain, eyes and nostrils in bony fishes and all land living vertebrates. The bones are derived from dermal bone, hence the alternative name dermatocranium...
of the skull is more loose in the lower vertebrates
Anamniotes
The anamniotes are an informal group of vertebrates that lack the amnion during fetal development. These animals are not able to have embryos that develop on land, thus they lay their eggs in water exclusively...
. In Agnathans and Chondrichthyes
Chondrichthyes
Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nares, scales, two-chambered hearts, and skeletons made of cartilage rather than bone...
, the skull lacks the skull roof
Skull roof
The skull roof , or the roofing bones of the skull are a set of bones covering the brain, eyes and nostrils in bony fishes and all land living vertebrates. The bones are derived from dermal bone, hence the alternative name dermatocranium...
dermal elements, their whole cranium being composed of the endocranium, properly called a chondrocranium
Chondrocranium
The chondrocranium is the primitive cartilaginous skeletal structure of the fetal skull that grows to envelop the rapidly growing embryonic brain....
. In most Osteichthyes
Osteichthyes
Osteichthyes , also called bony fish, are a taxonomic group of fish that have bony, as opposed to cartilaginous, skeletons. The vast majority of fish are osteichthyes, which is an extremely diverse and abundant group consisting of over 29,000 species...
, the skull is only loosely joined, and the endocranial elements do not form a unit with the skull roof.
Fossilization
An endocast or endocranial cast is a cast made of the mold formed by the impression the brainBrain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
makes on the inside of the neurocranium (braincase), providing a replica of the brain with most of the details of its outer surface. Endocasts can also form naturally, when sediments fill the empty skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
, after which the skull is destroyed and the cast fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
ized. Scientists are increasingly utilizing computerized tomography scanning technology to create digital endocasts without damaging valuable specimens. This gives a 3D representation of the brain. Brain size and complexity can then be determined.
Endocasts were used for looking at the brains of Homo sapiens to find hemispheric specialization.