Skull

The skull, or cranium, is the bony structure that surrounds and protects the brain in all animals with backbones, known as vertebrates. It forms the front part of the axial skeleton and is made from several types of bone that join together at strong points called sutures. In humans, the skull has two main parts: the neurocranium, which houses the brain, and the facial skeleton, which supports the face.

The skull serves many important functions. It protects the brain from injury, provides places for muscles to attach, and creates spaces for the eyes, ears, nose, and mouth. These spaces help with vision, hearing, smelling, tasting, and eating. In some animals, such as ungulates and elephants, the skull also supports structures like horns, antlers, and tusks, which can help defend against predators or play a role in mating.

The word skull likely comes from an old Old Norse word, while the scientific term cranium has roots in Latin and Greek. Whether in humans or other animals, the skull is a remarkable example of how the body’s structure can protect vital organs while also supporting many senses and functions.

Structure

The human skull is the bone structure that forms the head in the human skeleton. It supports the structures of the face and forms a cavity for the brain. Like the skulls of other vertebrates, it protects the brain from injury.

The skull consists of three main parts: the neurocranium, the sutures, and the facial skeleton. The neurocranium, also called the braincase, forms a protective cavity that surrounds and houses the brain and brainstem. The facial skeleton is made of bones that support the face, including the mandible. The bones of the skull are joined by special joints called sutures, which allow a little flexibility.

In humans, the skull is made up of 22 bones in total—eight cranial bones and fourteen facial bones. These include important bones such as the occipital bone, temporal bones, parietal bones, and the sphenoid. The skull also has air-filled spaces called paranasal sinuses and openings known as foramina, with the largest being the foramen magnum, which lets the spinal cord pass through.

Development

The skull is a complex structure made from bones that form in two different ways. Some bones develop directly from connective tissue, while others start as cartilage and then turn into bone. At birth, a human skull is made of 44 separate pieces that gradually join together as the baby grows.

Babies are born with soft spots on their heads called fontanelles. These spots allow the skull to change shape during birth and as the brain grows. There are six fontanelles, and they slowly close as the skull bones fuse together. The front soft spot, called the anterior fontanelle, can stay open for up to eighteen months. During early growth, the skull is large compared to the rest of the body, and the facial bones are much smaller than in adults.

Clinical significance

Craniosynostosis is a condition where certain parts of a baby’s skull fuse too early, changing how the skull grows. This can lead to an unusual head shape and may affect brain development if not enough space is available for the brain to grow.

Injuries to the brain can be very serious, and the skull normally protects the brain well. However, sometimes pressure can build up inside the skull after an injury, which can be dangerous. Doctors have used a procedure called trepanning for thousands of years, where a small hole is made in the skull to help relieve this pressure. Today, this is known as a craniectomy. Recently, doctors have also used advanced technology, such as 3D-printed materials, to help repair skulls.

Society and culture

Artificial cranial deformation was a practice in some historic cultures where pressure was applied to an infant’s skull to change its shape. This began soon after birth and continued for several years.

The skull can tell scientists about a person’s past. Forensic experts and archaeologists study skull shapes and teeth to learn about people from history. For example, they have examined remains from places like Spitalfields in the UK and Jōmon shell mounds in Japan.

In the past, some people believed that the shape of the skull showed personality or intelligence. This idea, called phrenology, is no longer accepted as scientific.

Male and female skulls look different when fully grown. Male skulls are usually larger and stronger, while female skulls are smaller and lighter. There are also small differences in shape that help experts tell them apart.

The cephalic index measures the shape of the head by comparing its width to its length. People can be long-headed, medium-headed, or short-headed based on this measurement.

Terminology

The skull is the bony structure that protects the brain in vertebrates. In some fish and amphibians, it is made of a flexible material called cartilage. There are different parts to the skull, such as the endocranium, which is inside, and the pericranium, a membrane on the outside. Other terms like chondrocranium and epicranium describe early stages or layers of the skull.

History

Trepanning is one of the oldest known surgical practices, where a hole is made in the skull. Evidence of this practice comes from cave paintings and human remains. In a burial site in France that dates back to 6500 BCE, many prehistoric skulls show signs of having had trepanation holes.

Additional images

Here are some interesting skulls from different animals:

• African elephant skull in the Cleveland Museum of Natural History
• Vulture skull
• King cobra skull
• Goat skull
• Skull of Tiktaalik, an extinct genus transitional between lobe-finned fish and early tetrapods
• Centrosaurus skull