The Human Skeleton Notes

Contents

  1. Introduction
  2. Bone Biology
  3. Neurocranium
  4. Splanchnocranium
  5. Dentition
  6. Human vs. Non-Human
  7. Burial Excavation

Introduction

Osteology (the study of bones) is involved in forensics, archaeology, and paleontology.

An adult has around 206 bones, while a child has around 270 bones.

Bone Biology

Bone Composition and Function

Bone is 70-80% mineral (hydroxyapatite) and 20-30% organic (collagen). The collagen prevents the bone from becoming brittle.

Bone acts as both an organ and a tissue. As an organ, bone protects soft tissues; anchors muscles, tendons, and ligaments; and acts as levers for movement. As a tissue, bone produces blood cells and acts as a reservoir of nutrients (calcium, fat).

Bone Variation

Human bones vary widely. There are four main types of variation: ontogeny (development), sexual dimorphism, geography (population), and individual.

The human skeleton is constantly remodeling in response to stress. Wolff's Law states that bone is deposited where needed and resorbed where not needed.

Musculoskeletal System

Joints are the structure between bones. There are three main types of joints:

  1. Synovial joints are freely movable. They include ball-and-socket joints (hip), hinge joints (elbow, knee), saddle-shaped joints (thumb), and planar joints (wrist, foot arch).
  2. Cartilaginous joints are made of cartilage and allow limited movement. One example are growth plates, which temporarily connect growth centers in a single bone.
  3. Fibrous joints are immovable (cranial sutures).

Both ligaments and tendons are connective tissue made of collagen. Ligaments connect bone to bone to stabilize joints. Tendons connect muscle to bone to facilitate movement.

Cartilage is a flexible connective tissue found in joints. It is composed mostly of collagen.

Anatomy of Bones

Bones can be categorized based on their shape

  1. Long bones include the arms and legs
  2. Short bones include metacarpals (hands), phalanges (fingers), and clavicles (collarbones)
  3. Flat bones include the cranial vault, scapulae, sternum (breastbone), ribs, and innominate (hipbone)
  4. Irregular bones include carpals (wrists), tarsals (ankles), and vertebrae
  5. Sesamoid bones are small, round bones embedded in tendons, like the patella (kneecap)

Bones can also be categorized based on their internal structure

  1. Compact bone is hard and makes up the outer layer of bones
  2. Spongy (cancellous) bone is porous and makes up the inner layer of bones
  3. Subchondral bone is covered by cartilage in joints

The long bone has several areas:

  1. The epiphysis (end of bone) develops from secondary ossification centers
  2. The diaphysis (shaft) develops from the primary ossification center
  3. The metaphysis is the area between the epiphysis and diaphysis where growth plates are located
  4. The medullary cavity is the hollow center of the diaphysis that contains bone marrow

The periosteum is a membrane that covers the outer surface of bones. It contains blood vessels, nerves, and cells that help with bone growth and repair.

Histology

Histology is the study of tissues at the microscopic level.

The Haversian system (osteon) is the basic structural unit of compact bone. It consists of concentric layers (lamellae) of bone tissue surrounding a central canal (Haversian canal) that contains blood vessels and nerves. Within each lamella, there are small cavities called lacunae that house bone cells (osteocytes).

There are three primary types of bone cells:

  1. Osteoblasts lay new bones and become osteocytes
  2. Osteocytes live in lacunae and maintain bone tissue
  3. Osteoclasts resorb bone

Ossification

There are two types of ossification (bone formation):

  1. In intramembranous ossification, mesenchymal tissue is directly converted into bone.
  2. In endochondral ossification, a cartilage model is first formed and then replaced by bone. This process is responsible for the formation of most bones in the body.

Primary centers of ossification appear during fetal development and form the diaphysis. Secondary centers of ossification appear after birth and form the epiphyses.

The process of bone growth occurs through two main mechanisms:

  1. The bone grows in length at the growth plates located in the metaphysis.
  2. The bone grows in width with the help of nutrient foramen, or openings in the bone that allow blood vessels to enter.

Neurocranium

Frontal

Ectocranial

  1. Frontal eminence (original center of ossification)
  2. Temporal lines (appear when you grit your teeth)
  3. Brow ridge
  4. Supraorbital margin
  5. Supraorbital foramen or notch (passage for vessels)
  6. Glabella (between the eyebrows)
  7. Zygomatic process of the frontal (articulates with zygomatic bone)

Endocranial

  1. Sagittal sulcus
  2. Frontal crest
  3. Foramen cecum
  4. Meningeal grooves

Inferior view

  1. Ethmoidal notch (location of ethmoid bone)
  2. Lacrima fossa (location of lacrimal gland)
  3. Frontal sinuses

Variations

  1. Metopic suture

Compared to the parietals, the minengeal impressions are fainter and the endocranial surface is more undulating.

Parietal

Angles

  1. Frontal angle (90 degrees)
  2. Sphenoidal angle
  3. Occiptal angle (near the occipital bone)
  4. Mastoid angle (near the mastoid process)

Ectocranial

  1. Parietal boss
  2. Parietal foramen (near the sagittal suture)
  3. Parietal striae (away from the sagittal suture)
  4. Temporal lines (extending from the frontal bone)

Endocranial

  1. Sagittal sulcus
  2. Sigmoid sulcus (near the mastoid angle)
  3. Meningeal grooves

Variations

  1. Bregmatic bone
  2. Wormian bones

Occipital

Ectocranial

  1. External occipital protuberence
  2. Highest, superior, and inferior nuchal lines
  3. External occipital crest (leading to the foramen magnum)
  4. Foramen magnum ("big hole")
  5. Occipital condyle (bean-shaped and articulates with C1)
  6. Condylar foramen (superior to the condyles)
  7. Hypoglossal canal (inferior to the condylar foramen)

Endocranial

  1. Cruciform eminence
  2. Cerebral fossa (triangular)
  3. Cerebellar fossa (quadrangular)
  4. Sagittal sulcus (usually swings right)
  5. Transverse sulcus (opp. sagittal sulcus)
  6. Internal occipital crest (leading to the foramen magnum)
  7. Jugular notch (below the foramen magnum)
  8. Middle meningeal grooves

Variations

  1. Inca bone
  2. Apical bone

Temporal

There are four parts of the temporal bone: squama, mastoid (right behind the ear), petrous (pyramid), and tympanic (inside).

Ectocranial

  1. Zygomatic process (and articulates with zygomatic bone)
  2. Articular eminence (right below the zygomatic process)
  3. Mandibular fossa (right next to the articular eminence)
  4. Post-glenoid process (small cone behind the mandibular fossa)
  5. Suprameatal crest (root of zygomatic process above the EAM)
  6. Supramastoid crest (extension of the suprameatal crest)
  7. Parietal notch (end of the crest that is level with the zygomatic process)
  8. Mastoid process (behind the ear)
  9. Mastoid notch (behind the mastoid process)
  10. Mastoid foramen
  11. External acoustic meatus (EAM)

Endocranial (posterior view)

  1. Internal acoustic meatus (biggest hole on the inside)

Endocranial (inferior view)

  1. Styloid process (pointed projection)
  2. Styloidmastoid foramen (under the styloid process)
  3. Jugular fossa (bottom-right of the styloid process)
  4. Cartoid canal (above the styloid process)

Splanchnocranium

Auditory Ossicles

  1. Stapes (stirrup)
  2. Incus (anvil)
  3. Malleus (hammer)

Sphenoid

The sphenoid is comprised of the body, lesser wings, greater wings, and the pterygoid process.

Sphenoid

Superior view

  1. Anterior clinoid process (hooks under the wings)
  2. Sella turcica (between the wings)
  3. Pituitary fossa (under the Sella turcica)
  4. Dorsum sellae (handlebars)
  5. Posterior clinoid process (ends of handlebars)
  6. Clivus (under the posterior clinoid process)
  7. Body (under the dorsum sellae)

Superior View (OOROS)

  1. Optic canal
  2. Superior orbital fissures
  3. Foramen rotundum (round)
  4. Foramen ovale (oval)
  5. Foramen spinosum (tiny)

Anterior View

  1. Orbital surfaces
  2. Sphenoidal crest
  3. Sphenoidal sinus (holes on either side of the crest)
  4. Sphenoidal rostrum (under the sphenoidal crest)

Anterior View (Pterygoid process)

  1. Medial pterygoid plate
  2. Pterygoid hamulus (hook on the medial pterygoid plate)
  3. Lateral pterygoid plate
  4. Pterygoid fossa (formed by the medial and lateral plates)

Ethmoid

  1. Crista galli (projection)
  2. Cribriform plate (horizontal plate)
  3. Perpendicular plate
  4. Lateral mass (labyrinth touching eye sockets)

Inferior Nasal Concha

Can see through the nasal cavity, on the sides. The maxillary process is the part that is hooked onto the side of the nasal aperture. The head is anterior and the long tail inferior. It's like a fish coming out.

Nasal

Makes up the bridge of the nose. The top that articulates with the frontal is thicker. The distal is longer than the medial.

Lacrimal

Inside of the eye socket, near the nose. The hook forms the grooves for the lacrimal glands.

Zygomatic

  1. Frontal process
  2. Orbital margin
  3. Temporal process
  4. Maxillary process
  5. Masseteric origin (masseter muscle attaches)
  6. Zygomaticofacial foramen

The anterior surface is big and flat and will have a zygomaticofacial foramen.

Maxilla

Anterior View

  1. Frontal process
  2. Zygomatic process
  3. Infraorbital foramen (next to zygomatic process)
  4. Canine jugum (from the canine root)
  5. Canine fossa (posterior to the canine jugum)
  6. Anterior nasal spine (near the nasal cavity)
  7. Alveolar process (houses the teeth)
  8. Alveolar canals (tooth sockets)

Superior view

  1. Anterior lacrimal crest (near lacrimals)
  2. Infraorbital sulcus (in the orbitals)

Posterior view

  1. Maxillary sinus
  2. Palatine process (roof of mouth)
  3. Incisive foramen (right behind incisors)

Canine root is distinctive to anatomically modern humans. Humans have relatively flat faces; premaxilla fuse with maxilla.

Palatine Bone

Shaped like an L. The shorter part is the horizontal plate and should be oriented medially. The longest part is the vertical plate. The posterior has a ridge sticking out called the pyramidal process.

  1. Posterior nasal spine
  2. Pyramidal process
  3. Greater palatine foramen (anterior)
  4. Lesser palatine foramen (posterior)

Vomer

Divides the nasal aperture in half. The anterior is thin and the posterior is thick.

Mandible

The mandible is divided into the body (corpus) and the ascending ramus.

External surface

  1. Mental eminence (chin)
  2. Mental foramen
  3. Alveolar process
  4. Alveolar canals

Internal surface

  1. Mandibular foramen
  2. Lingula (sticks up next to mandibular foramen)
  3. Mylohyoid line
  4. Submandibular fossa (below the mylohyoid line)
  5. Mylohyoid groove (below the mylohyoid groove and runs up to the mandibular foramen)
  6. Mental spines (near the chin)
  7. Digastric fossa (inferior and posterior to mental spines)

External surface

  1. Ascending ramus
  2. Masseteric tuberosity (rough)
  3. Gonial angle
  4. Mandibular condyle
  5. Condylar neck
  6. Coronoid process
  7. Mandibular notch

Internal surface

  1. Pterygoid tuberosity

The mental eminence is a distinctive feature of anatomically modern humans.

Men tend to have a more 90° gonial angle, while women tend to have a more obtuse gonial angle. Older individuals with tooth loss also tend to have a more obtuse gonial angle.

Dentition

Terms

  1. Mesial is toward the midline and distal is away from the midline
  2. Labial is toward the lips and buccal is toward the cheek
  3. Lingual is toward the tongue
  4. Interproximal is where two teeth meet
  5. Incisal and occlusal are biting surfaces

Humans are diphyodont, which means that they have two sets of teeth, deciduous (baby) and permanent.

Humans are also heterodonts, which means that we have different types of teeth:

  1. Incisors
  2. Canines
  3. Premolars
  4. Molars

Incisors are used for cutting, canines for tearing, premolars for grinding, and molars for crushing.

Teeth Anatomy

Teeth have two parts: the crown and the root. Teeth have three layers: enamel, dentine, and pulp chamber. Connective tissue called cementum holds the teeth in place.

Teeth grow from the cusp to the cemento-enamel junction (CEJ). Roots are the last to form. Ameloblast deposit enamel at the same time as adontoblast deposit dentine.

Enamel is 96% mineral. Dentine is 70% mineral and 30% collagen. The pulp chamber is mostly nerves and blood vessels.

Adults have 32 teeth. There are four quadrants in the mouth, each with 8 teeth: 2 incisors, 1 canine, 2 premolars, and 3 molars. The third molars are the wisdom teeth. Many people have the third molar pulled out because they cause crowding.

Identifying Teeth

Upper incisors are generally larger, broader, and more likely to be shovel-shaped. Upper incisor roots are more circular, while lowers are more compressed. Incisors tend to be more 90 degree mesially and curved distally.

Canines tend to come to a point and tend to be wider than incisors. Upper canines are generally larger, broader, and more likely to have cingulum than the lowers.

Premolars are also called bicuspids because they have two cusps. Lowers have a larger buccal cusp than lingual cusp. Uppers sometimes have two roots (often fused).

Upper molars usually have 3 roots and 3-4 major cusps. Lower molars generally have 2 roots and 4-5 major cusps. The uppers tend to be square in shape while the lowers tend to be rectangular or oblong. They are slightly narrow buccally and wider lingually. Uppers tend to be more asymmetric around the mesiodistal axis than lowers. This is because uppers have triangular hypocone on the lingual distal end. This hypocone is largest on the first molar and smaller on the second and third.

To side the teeth, note that the roots swing distally.

Human vs. Non-Human

Our bones tend to be more dense and less trabeculae in the ends than non-humans.

Subadults

  • Smaller
  • Unfused epiphyses
  • Porous, especially at the ends

Burial Excavation

  1. Pedestaling involves removing the dirt while leaving the skeleton and the items in place.
  2. Documentation involves taking photographs, photogrammetry, drawing the site.
  3. Lift