Why does the clavicle ossify intramembraneously?

Why does the clavicle ossify intramembraneously?

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The clavicle is the only long bone which ossifies as a membrane bone. I studied this process, but I can't find the reason why it features intramembraneous ossification?

Why does the clavicle ossify intramembraneously? - Biology

Ossification, or osteogenesis, is the process of bone formation by osteoblasts. Ossification is distinct from the process of calcification whereas calcification takes place during the ossification of bones, it can also occur in other tissues. Ossification begins approximately six weeks after fertilization in an embryo. Before this time, the embryonic skeleton consists entirely of fibrous membranes and hyaline cartilage. The development of bone from fibrous membranes is called intramembranous ossification development from hyaline cartilage is called endochondral ossification. Bone growth continues until approximately age 25. Bones can grow in thickness throughout life, but after age 25, ossification functions primarily in bone remodeling and repair.

What is Endochondral Ossification

Endochondral ossification is a type of ossification that proceeds through the formation of intermediate cartilage. Generally, this intermediate cartilage is hyaline cartilage. Here, the cartilage only serves as a template. Endochondral ossification is involved in the formation of long bones as well as the bones at the base of the skull.

Figure 1: Endochondral Ossification

Endochondral Ossification of Long Bones – Steps

  1. Around 6-8 weeks after conception, mesenchymal cells differentiate into chondrocytes, which form the cartilaginous bone precursor. Perichondrium, which is the envelope of the cartilage appears soon after the formation of the cartilage.
  2. The matrix of the cartilage calcifies. This results in the death of chondrocytes and blood vessels invade through the forming spaces called lacuna.
  3. The osteogenic cells also migrate into the spaces and become osteoblasts.
  4. Penetration of the growing cartilage by blood capillaries initiates the transformation of perichondrium into the bone-producing periosteum.
  5. In the compact bones, osteoblasts form a periosteal collar/bone collar around the shaft of the log bone called the diaphysis.
  6. Within the second or third month of the fetal life, ossification ramps up, creating the primary ossification center deep in the periosteal collar where ossification begins.
  7. In the meanwhile, chondrocytes grow the cartilage at the two ends of the bone, increasing the length.
  8. When the skeleton fully forms, the cartilage can be found between the diaphysis and epiphysis as the epiphyseal plate and at the joint surface as articular cartilage.
  9. After birth, a secondary ossification center forms at the epiphyseal plate, which helps the longitudinal growth of bone.

Xiphoid Process of Sternum

The xiphoid process is the smallest and most inferior region of the sternum, or breastbone. At birth, it is a thin, roughly triangular region of cartilage that slowly ossifies into a bone and fuses with the body of the sternum. Clinically, the xiphoid process plays an important role as a bony anatomical landmark in the trunk and may be damaged by improperly administered CPR.

The xiphoid process is located inferior to the body of the sternum. The word xiphoid comes from the Greek word for “sword-shaped,” which describes its thin and pointed shape. Continue Scrolling To Read More Below.

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  • Perforation with a small foramen in its center
  • Bifurcation with a split into left and right branches at its inferior end.

These variations in anatomy apparently do not result in any sort of change in the function of the xiphoid process and may be inherited genetically.

Developmentally, the xiphoid process begins as a structure made of hyaline cartilage at birth and childhood, slowly ossifying into a bony part of the sternum. In fact, the ossification of the xiphoid process is so slow that it often does not end until an individual reaches the age of 40.

The xiphoid process functions as a vital attachment point for several major muscles. It acts as one of several origins for the diaphragm muscle that forms the floor of the ribcage and performs the vital process of respiration. The xiphoid process also acts as an insertion for the rectus abdominis and transverse abdominis muscles that compress and flex the abdomen. During cardiopulmonary resuscitation (CPR), the xiphoid process may be used as a bony landmark to determine the location for administering chest compressions. It is extremely important that pressure is not exerted on the xiphoid process during chest compressions, as this can cause the xiphoid process to separate from the sternum, possibly puncturing the diaphragm or liver.

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How Bones Grow in Length

The epiphyseal plate is the area of elongation in a long bone. It includes a layer of hyaline cartilage where ossification can continue to occur in immature bones. We can divide the epiphyseal plate into a diaphyseal side (closer to the diaphysis) and an epiphyseal side (closer to the epiphysis). On the epiphyseal side of the epiphyseal plate, hyaline cartilage cells are active and are dividing and producing hyaline cartilage matrix. (figure 6.43, reserve and proliferative zones). On the diaphyseal side of the growth plate, cartilage calcifies and dies, then is replaced by bone (figure 6.43, zones of hypertrophy and maturation, calcification and ossification). As cartilage grows, the entire structure grows in length and then is turned into bone. Once cartilage cannot grow further, the structure cannot elongate more.

The epiphyseal plate is composed of five zones of cells and activity (Figure 6.4.3). The reserve zone is the region closest to the epiphyseal end of the plate and contains small chondrocytes within the matrix. These chondrocytes do not participate in bone growth but secure the epiphyseal plate to the overlying osseous tissue of the epiphysis.

Figure 6.4.3 – Longitudinal Bone Growth: The epiphyseal plate is responsible for longitudinal bone growth.

The proliferative zone is the next layer toward the diaphysis and contains stacks of slightly larger chondrocytes. It makes new chondrocytes (via mitosis) to replace those that die at the diaphyseal end of the plate. Chondrocytes in the next layer, the zone of maturation and hypertrophy, are older and larger than those in the proliferative zone. The more mature cells are situated closer to the diaphyseal end of the plate. The longitudinal growth of bone is a result of cellular division in the proliferative zone and the maturation of cells in the zone of maturation and hypertrophy. This growth within a tissue is called interstitial growth.

Most of the chondrocytes in the zone of calcified matrix, the zone closest to the diaphysis, are dead because the matrix around them has calcified, restricting nutrient diffusion. Capillaries and osteoblasts from the diaphysis penetrate this zone, and the osteoblasts secrete bone tissue on the remaining calcified cartilage. Thus, the zone of calcified matrix connects the epiphyseal plate to the diaphysis. A bone grows in length when osseous tissue is added to the diaphysis.

Bones continue to grow in length until early adulthood. The rate of growth is controlled by hormones, which will be discussed later. When the chondrocytes in the epiphyseal plate cease their proliferation and bone replaces all the cartilage, longitudinal growth stops. All that remains of the epiphyseal plate is the ossified epiphyseal line (Figure 6.4.4).

Figure 6.4.4 – Progression from Epiphyseal Plate to Epiphyseal Line: As a bone matures, the epiphyseal plate progresses to an epiphyseal line. (a) Epiphyseal plates are visible in a growing bone. (b) Epiphyseal lines are the remnants of epiphyseal plates in a mature bone. EDITOR’S NOTE: you should add an xray of a epiphyseal plate vs line


We are grateful to M. Herbin, C. Bens, F. Renoult, C. Denys, and J. Cuisin (Museum National d'Histoire Naturelle, Paris), Peter Giere and Frieder Mayer (Museum für Naturkunde, Berlin), Paula Jenkins and Roberto Portela Miguez (Natural History Museum, London), and their colleagues for access to comparative material. For access to material and facilities, we thank Frank Knight (University of Ozarks, AK), Richard Truman (Louisiana State University School of Veterinary Medicine, Baton Rouge, LA), the Laboratory of Paleontology, and the Institut des Sciences de l'Evolution de Montpellier. We thank Emily Buchholtz for her comments on the manuscript. A. Heaver (University of Cambridge), N. Karjilov (Helmholtz Zentrum Berlin), R. Abel (Natural History Museum), R. Lebrun (Institut des Sciences de l'Evolution de Montpellier), K. Lin (Harvard University), F. Landru, C. Morlier, G. Guillemain, and the staff from Viscom SARL (St. Ouen l'Aumône, France) provided generous help and advice with CT acquisition. We thank Mariella Superina for her help and advice in finding ontogenetical series of xenarthrans. We thank Boris Brasseur for providing living accommodation in Paris. We are also indebted to two anonymous reviewers and the editors for their contribution to improve the manuscript. We thank Mariella Superina for her help and advice in finding ontogenetical series of xenarthrans. We thank Boris Brasseur for providing living accommodation in Paris. We acknowledge financial support from Grant F/09 364/I from the Leverhulme Trust.


Tim D. White , Pieter A. Folkens , in The Human Bone Manual , 2005

10.1.1 Anatomy

The sternum, or breastbone, functions at its upper end to connect the shoulder girdle (clavicle and scapula) to the thorax. In addition, it anchors the anterior ends of paired ribs 1–7 via cartilage. The bone is composed of three main parts in adulthood but develops from six segments. The segment joints may all fuse in adulthood, but their location is indicated by costal notches along each side of the sternum.

Figure 10.1 . Sternum, anterior. The xiphoid process on this sternum had not ossified and is not shown. Superior is up. Natural size.

Figure 10.2 . Sternum, left lateral. Superior is up. Natural size.

Figure 10.3 . Sternum, posterior. Superior is up. Natural size.

The manubrium is the most massive, thickest, and squarest of three main sternal elements. It is the superior-most element of the sternum and is the widest part of this bone.

Clavicular notches occupy the superior corners of the sternum. It is here that the manubrium articulates with the right and left clavicles.

The jugular (suprasternal) notch is the midline notch on the superior border of the manubrium.

Costal notches occupy both sides of the manubrium inferior to the clavicular notches. These notches represent articulations with the costal cartilages of the first ribs. The manubrium shares articulation for the second ribs with the corpus sterni.

The corpus sterni is the central part, the body, or blade, of the sternum. It is formed during ontogeny from the fusion of sternal segments (sternebrae) 2–5. The corpus sterni may fuse, partially fuse, or remain unfused with the manubrium in adulthood.

The sternal angle is the angle formed between the fused manubrium and the corpus sterni.

The costal notches along either side of the corpus sterni are for articulation with the costal cartilages of ribs 2–7.

Lines of fusion are often apparent between the sternebrae. These lines pass horizontally through the right and left costal notches for ribs 3–5.

In 5–10% of adult corpora sternorum a midline foramen, the sternal foramen, perforates the sternal body.

The xiphoid process is the variably ossified inferior tip of the sternum. It often fuses with the corpus sterni in older adults. It shares the seventh costal notch with the body. This process can be partially ossified and may ossify into bizarre asymmetrical shapes with odd perforations. In short, the xiphoid is a highly variable element. The xiphoid process of the individual chosen to illustrate this text, for example, was not ossified at the time of death.

Fracture and Dislocation: The wrist is most frequently injured among all joints in the human body [16] . Due to their position in the hand, the carpal bones often get fractured or dislocated as a result of accidents, like falling on an outstretched hand [17] , and sports injuries, especially when playing sports like hockey and tennis. One characteristic symptom of a broken or dislocated carpal bone is that the pain gets worse with movement [18]. The scaphoid is the most commonly fractured carpal bone, while the most common forms of dislocations in this area involve the lunate [16] .

Carpal Tunnel Syndrome: Another common condition involving the wrist, the carpal tunnel syndrome occurs when the medial nerve gets compressed in its passage through the wrist. It usually causes a characteristic pain, numbness, and tingling sensation in the fingers (may not be as prominent in the little finger) [19] .

Carpal Avascular Necrosis: A condition where a lack of blood supply to the carpal bone cells causes serious damage, finally resulting in their death. The lunate and scaphoid are most prone to this degenerating disorder [20] .

Other conditions that may involve the wrist include torn ligaments, arthritis, overuse injuries, and joint infections [21] .

Mechanisms of bone development and repair

Bone development occurs through a series of synchronous events that result in the formation of the body scaffold. The repair potential of bone and its surrounding microenvironment — including inflammatory, endothelial and Schwann cells — persists throughout adulthood, enabling restoration of tissue to its homeostatic functional state. The isolation of a single skeletal stem cell population through cell surface markers and the development of single-cell technologies are enabling precise elucidation of cellular activity and fate during bone repair by providing key insights into the mechanisms that maintain and regenerate bone during homeostasis and repair. Increased understanding of bone development, as well as normal and aberrant bone repair, has important therapeutic implications for the treatment of bone disease and ageing-related degeneration.


The hyoid bone is small, and it functions as an attachment point for many muscles involved in swallowing, jaw movements, and respiration.

Swallowing function may be impaired due to problems such as stroke, neck injuries, or jaw and neck cancers. If that occurs, working with a specialist like a speech pathologist may be useful.

Your speech therapist may perform specific exercises to help you swallow better, and these may involve getting familiar with your hyoid bone. Exercises for swallowing function may include:  

Your therapist may also teach you how to mobilize your hyoid bone and to stretch or strengthen the muscles that surround it.