The endocranium in

comparative anatomy Comparative anatomy is the study of similarities and differences in the anatomy of different species. It is closely related to evolutionary biology and phylogeny (the evolution of species). The science began in the classical era, continuing in t ...

is a part of the

skull base The base of skull, also known as the cranial base or the cranial floor, is the most Anatomical terms of location#Superior and inferior, inferior area of the human skull, skull. It is composed of the endocranium and the lower parts of the Calvaria ...

vertebrates Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

and it represents the basal, inner part of the

cranium The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

. The term is also applied to the outer layer of the dura mater in

human anatomy Human anatomy (gr. ἀνατομία, "dissection", from ἀνά, "up", and τέμνειν, "cut") is primarily the scientific study of the morphology of the human body. Anatomy is subdivided into gross anatomy and microscopic anatomy. Gross ...

Structure

Structurally, the endocranium consists of a boxlike shape, open at the top. The posterior margin exhibits the '' foramen magnum'', an opening for the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...

. The floor of the endocranium has several paired openings for the

cranial nerves Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and f ...

, and the anterior margin holds a spongy construction, allowing for the external nasal nerves to pass through. Romer, A.S. & T.S. Parsons. 1977. ''The Vertebrate Body.'' 5th ed. Saunders, Philadelphia. (6th ed. 1985) All bones of the structure derive from the

cranial neural crest The cranial neural crest is one of the four regions of the 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. The endocraniu ...

during

fetal development Prenatal development () involves the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal deve ...

Endocranial elements in humans

In humans and other

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s, the endocranium forms during

as a cartilaginous

neurocranium In human anatomy, the neurocranium, also known as the braincase, brainpan, brain-pan, or brainbox, is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the cal ...

, that ossifies from several centers. Several of these bones merge, and in the adult

primate Primates is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...

s (including humans), the endocranium is composed of only five bony elements (from front to back):'' Colbert, E.H. & Morales, M. (2001): Colbert's Evolution of the Vertebrates: A History of the Backboned Animals Through Time''. 4th edition. John Wiley & Sons, Inc, New York - . * The

ethmoid The ethmoid bone (; from ) is an unpaired bone in the skull that separates the nasal cavity from the brain. It is located at the roof of the nose, between the two orbit (anatomy), orbits. The cubical (cube-shaped) bone is lightweight due to a sp ...

bone, lying behind the nose. * The

sphenoid bone The sphenoid bone is an unpaired bone of the neurocranium. It is situated in the middle of the skull towards the front, in front of the basilar part of occipital bone, basilar part of the occipital bone. The sphenoid bone is one of the seven bon ...

, underlying the forward portion of the brain * Paired

petrous part of the temporal bone The petrous part of the temporal bone is pyramid-shaped and is wedged in at the base of the skull between the sphenoid and occipital bones. Directed medially, forward, and a little upward, it presents a base, an apex, three surfaces, and three ...

s, containing the

inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the ...

structures * Most of the

occipital bone The occipital bone () is a neurocranium, cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone lies over the occipital lob ...

, surrounding the ''foramen magnum''

Other animals

Endocranial components in other tetrapods

The endocranium in

s is much reduced in relative size and number of bones compared to the condition in the ancestral land vertebrates, though the

occur as one or more stout bony elements in several mammal groups. The occipital bone is also found as several bony elements in

birds Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

and

reptiles Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...

, while the skull of modern

amphibian Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...

s is generally reduced with a simplified endocranium. The skull of early

labyrinthodonts "Labyrinthodontia" (Greek language, Greek, 'maze-toothed') is an informal grouping of Extinction, extinct predatory amphibians which were major components of ecosystems in the late Paleozoic and early Mesozoic eras (about 390 to 150 million years ...

were rather complex, and contained in addition to the bones mentioned above several small cartilaginous 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 fish

While the endocranium is an integral part of the skull in mammals,

and

, its connection to the roofing parts of the skull is more loose in the lower vertebrates. In Agnathans and

Chondrichthyes Chondrichthyes (; ) is a class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fish'', which have skeleto ...

, the skull lacks the

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, including land-living vertebrates. The bones are derived from dermal bone and are part of the dermatocranium. In com ...

dermal elements, their whole cranium being composed of the endocranium, properly called a chondrocranium. In most

Osteichthyes Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...

, 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

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

makes on the inside of the

(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 The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

, after which the skull is destroyed and the cast

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

ized. Scientists are increasingly utilizing

computerized tomography A computed tomography scan (CT scan), formerly called computed axial tomography scan (CAT scan), is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or ...

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.

References

{{Reflist Human anatomy Vertebrate anatomy