Endocranium

Human endocranium (pink fields), inner surface

The loosely connected skull of a perch.

The endocranium, a crucial anatomical structure, finds its position as a foundational element of the vertebrate skull. When studied under the lens of comparative anatomy, the endocranium reveals itself as the innermost part of the cranium, predominantly contributing to the skull base. Not limited to vertebrate anatomy, the term also sees its application in human anatomy, where it's associated with the outermost layer of the dura mater.

Comparative Anatomy

Vertebrates

In the vast realm of vertebrates, the endocranium constitutes the basal and internal portion of the cranium. It plays an instrumental role by:

• Protecting the brain and supporting its weight.
• Housing various cranial nerves and blood vessels.
• Serving as the anchor point for several muscles.

Different vertebrate species have endocrania that vary in terms of size, thickness, and complexity, based on their ecological and evolutionary adaptations.

Humans

The term "endocranium" takes on a slightly different meaning in human anatomy. Here, it describes the outermost layer of the dura mater – the thickest membrane that envelopes the brain.

Structure and Composition

Composed predominantly of compact bone, the endocranium, particularly in vertebrates, is further partitioned into:

• Basicranium: This is the floor of the skull, often associated with the formation of the base.
• Alisphenoid: Found in mammals, this section forms part of the temporal bone, located near the sphenoid bone.
• Basioccipital: Located posteriorly, this bone fuses with others during development to contribute to the occipital bone.

In humans, the endocranial layer of the dura mater is dense and fibrous, serving as the final protective barrier before one reaches the brain tissue.

Function

Apart from offering structural support and protection, the endocranium performs several other functions:

• Enclosure of the Brain: It forms a protective bony vault around the brain.
• Attachment: Various ligaments and tendons attach to the endocranium, aiding in stability.
• Facilitation of Blood Flow: Channels and grooves in the endocranium guide blood vessels, ensuring adequate brain oxygenation.

Evolutionary Perspective

From an evolutionary standpoint, the development of the endocranium mirrors the evolutionary advancements of vertebrates, particularly in relation to brain size and complexity. Fossils and comparative studies of endocrania across species provide invaluable insights into evolutionary trends and ancestral lineages.

See also

• Cranium
• Dura mater
• Skull
• Comparative anatomy

References

• Parker, T.J. & Haswell, W.A. (1921). A Textbook of Zoology. London: Macmillan and Co.
• Romer, A.S. (1966). Vertebrate Paleontology. Chicago: University of Chicago Press.
• Standring, S. (2016). Gray's Anatomy: The Anatomical Basis of Clinical Practice. Elsevier Health Sciences.