It provides protection and strength to bones. The osteon is formed by . The compact bone also provide strong mechanical levers, against which the muscles can create movement. Is it easy to get an internship at Microsoft? Such roundish unit is called OSTEON. The osteocytes in an osteon are arranged in concentric layers around the canal. ___ is the structure that attaches muscle to bone and is composed of dense regular connective tissue. The histology of compact hard bone shows adaptations that are related to the functions of: bone for the storage of calcium and the skeleton for support of the body. . Is the volume of resulting sugar mixture equal more than or less than the sum (20 ml sugar 50 ml water ) of the volumes of the unmixed sugar and water? The Cellular Level of Organization, Chapter 4. In these studies, a dye containing a radioactive ion is injected into the body. a. dense regular b. bone c. blood d. areolar e. simple columnar, Bone tissue can be described as the _____. 3) Mesoderm. Compact bones are also known as cortical bones. A hollow medullary cavity filled with yellow marrow runs the length of the diaphysis of a long bone. The structural unit of compact bone is the: a. osteon b. canaliculus c. lacuna. Blood vessels and nerves enter the bone through the nutrient foramina to nourish and innervate bones. Skeletal system part 1. Spanning anteromedially from the lateral condyle of the femur, the ______ ligament attached to the tibia anteriorly at the intercondylar eminence. Bone Tissue and the Skeletal System, Chapter 12. 6 What are some characteristics of spongy bone? The sound leakage problem of bluetooth bone conduction headphones is mainly due to the fact that they convert sound into mechanical vibration through the sound unit, and vibrate the bone to transmit sound. Match the terms with the functions given below: The compact bone is the main structure in the body for support, protection, and movement. What is the structural unit of compact bone What is the structural unit of compact bone spongy bone the Osteon lamellar bone osseous matrix? Compact bone is laid in such a manner that there are histological units seen in cross section. Osteoblasts, which do not divide, synthesize and secrete the collagen matrix and other proteins. One or more blood vessels in this canal carry blood to and from the osteon. 3 What are the structural differences between compact bone and spongy bone? Later discussions in this chapter will show that bone is also dynamic in that its shape adjusts to accommodate stresses. Bone is hard and many of its functions depend on that characteristic hardness. What is the basic unit of compact bone? What characterizes the periosteum. c. compact bone. Haversian Moreover, it is a storehouse of calcium and hosphorus. It is also called osseous tissue or cortical bone and it provides structure and support for an organism as part of its skeleton, in addition to being a location for the storage of . b. Hyaline cartilage c. Epithelium d. Fibrocartilage e. Dense re. A) Osteon B) Haversian system C) Osteolyces D) Both A and B Question 2 _____ records can be compared to teeth in the skull to help identify a body. hbspt.cta._relativeUrls=true;hbspt.cta.load(189659, '7da024a9-4451-44f6-a682-29eaf2d8974b', {"useNewLoader":"true","region":"na1"}); hbspt.cta._relativeUrls=true;hbspt.cta.load(189659, 'd81c2b40-64cb-4f78-a901-2d949123900d', {"useNewLoader":"true","region":"na1"}); When you select "Subscribe" you will start receiving our email newsletter. What are the Easy Home Remedies To Reduce Weight? What bones function primarily to provide support? In what ways is the structural makeup of compact and spongy bone well suited to their respective functions? The diagram above shows a transverse view of an osteon (Haversian system) the basic unit of compact bone. d) spongy bones. This canal contains one or more blood vessels that carry blood to and from the osteon. Most studied answer. C) osteons. The osteons are arranged in multiple layers or A) spongy B) osteon C) compact D) lamellar E) irregular. What are the three smallest bones in the human body? Bone matrix provides bones with their basic structure. . b. periosteum c. endosteum d. epiphysis. All rights reserved. What is the basic functional units of compact bone? A projection is an area of a bone that projects above the surface of the bone. The basic functional unit of compact bone is the: osteoblast osteon osteoclast osteocyte - Answered by a verified Tutor. We also use third-party cookies that help us analyze and understand how you use this website. What is the role of bone in calcium homeostasis? Are you an instructor? . The wider section at each end of the bone is called the epiphysis (plural = epiphyses), which is filled internally with spongy bone, another type of osseous tissue. What forms the largest portion of the coxal bone? This type of bone tissue surrounds the medullary cavity: _____. D) canaliculi. b) compact bone. Our experts can answer your tough homework and study questions. What is the structural and functional unit of compact bone quizlet? When the bone stops growing in early adulthood (approximately 1821 years), the epiphyseal plate becomes an epiphyseal line seen in the figure. A. d) has many spaces and lacks osteocytes. If the articular cartilage at the end of one of your long bones were to degenerate, what symptoms do you think you would experience? These multinucleated cells originate from monocytes and macrophages, two types of white blood cells, not from osteogenic cells. The periosteum is composed of dense irregular connective tissue. What is the basic structural unit of a bone? What is the tarsal bone that articulates with the tibia? As the name implies, an articulation is where two bone surfaces come together (articulus = joint). copyright 2003-2023 Homework.Study.com. Bone remodelling relies on the correct function of two . What are the six functions of the skeletal system? Compact bone (or cortical bone) forms the hard external layer of all bones and surrounds the medullary cavity, or bone marrow. Blood C. Bone D. Simple columnar E. Areolar, The type of bone that is adapted to withstand stresses that arrive from many directions is [{Blank}] bone. Therefore, reconstruction of the osteon structure is . When occurring in the skull, Pagets disease can cause headaches and hearing loss. C) dura mater. Classify the bones in the following diagram according to their shape. a. Spongy bone. Supportive connective tissues (bone and cartilage) have cells that live in small cavities in the solid matrix. Tendons and ligaments attach to bones at the periosteum. Give examples. The cellular layer is adjacent to the cortical bone and is covered by an outer fibrous layer of dense irregular connective tissue (see Figure 6.3.4a). These cookies track visitors across websites and collect information to provide customized ads. Within flat bones, dipole is another name for the: a. dense connective tissue covering the bone. What is the function of the parietal bone? Bone tissue (osseous tissue) differs greatly from other tissues in the body. The structural aspects of compact bone tissue are: 1. What is the basic functional unit of compact bone? (a) Volkmann's canals. This cookie is set by GDPR Cookie Consent plugin. Wiki User. calcium ion concentration in body fluids? C) concentric lamellae. As part of Human Anatomy Atlas 2022 +'s May 2022 update, we released a revamped osteon model, adding more detail in the central canal and the concentric lamellae . Consider the extent of secondary fracturing with respect to where on the bone this is located. 4 What is the structure and function of compact bone? What part of a long bone is not covered by the periosteum? FROM THE STUDY SET. They function as a buffer system to the compact bone and support its function. Which is greater 36 yards 2 feet and 114 feet 2 inch? Compact bone (or cortical bone) forms the hard external layer of all bones and surrounds the medullary cavity, or bone marrow. Bone contains three types of cells: osteoblasts, which deposit bone; osteocytes, which maintain the bone; and osteoclasts, which resorb bone. What does the " form follows function" idea even mean when it is towards both compact bone and spongy bone? Which tarsal bone articulates with the tibia and fibula? See our privacy policy for additional details. The skeletal muscle as an entire organ is covered by: a. endomysium. Want a quick review of the structure of bone tissue? Spongy bone functions in _______. These cells are part of the outer double layered structure called the periosteum (peri = around or surrounding). The periosteum is secured to the underlying bone by dense connective tissue called: a) Perforating (Sharpey's) fibers. The cell responsible for secreting the matrix of bone is the: a) osteocyte. osteon, the chief structural unit of compact (cortical) bone, consisting of concentric bone layers called lamellae, which surround a long hollow passageway, the Haversian canal (named for Clopton Havers, a 17th-century English physician). It also contains a small amount of connective tissue. B) metaphysis. The parietal bones and occipital bone articulate at the [{Blank}] suture. The osteocytes in spongy bone are nourished by blood vessels of the periosteum that penetrate spongy bone and blood that circulates in the marrow cavities. The trabeculae are covered by the endosteum, which can readily remodel them. 2 What is the basic unit of compact bone? Sirona PCB DWV Compact water unit wiring, spare. Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet. 4) it helps heal bone fractures. To wrap it all up, osteons are structural and functional units of compact bone. The ongoing balance between osteoblasts and osteoclasts is responsible for the constant but subtle reshaping of bone. They have a cuboidal structure. Image quality looks comparable to the popular DJI FPV system, with time it might get even better with full Betaflight OSD support and 1080p resolution given the more capable hardware. a. Osteons (Haversian systems) b. Lamellae 2. Red bone marrow fills the spaces between the spongy bone in some long bones. A) osteoclast B) osteoblast C) progenitor cell D) osteocyte. In long bones, as you move from the outer cortical compact bone to the inner medullary cavity, the bone transitions to spongy bone. However, you may visit "Cookie Settings" to provide a controlled consent. Match the terms with the functions given below: Curious to know if you also object to firefighters passing out candy from their trucks in parades, military jets doing flyovers at large sporting events, and the Oklahoma Dept of Wildlife Conservation running a very funny Twitter account. What are the primary parts of a typical long bone? b. epiphysis. What's the smallest bone in the human body? system is a microscopic, structural unit of compact bone also Compact bone is the denser, stronger of the two types of osseous tissue (Figure 6.3.6). Compact bone is composed to spicules called trabeculae. A teacher walks into the Classroom and says If only Yesterday was Tomorrow Today would have been a Saturday Which Day did the Teacher make this Statement? Define and list examples of bone markings. The entire skeleton is laid down as a model before ossification sets in to harden it into bone. These surfaces tend to conform to one another, such as one being rounded and the other cupped, to facilitate the function of the articulation. This enables better protection of the product and lower shipping costs. The functional unit of compact bone tissue is the osteon. Be sure to subscribe to theVisible BodyBlog for more anatomy awesomeness! What are the short bones in the skeletal system? Figure 6.3.6 - Diagram of Compact Bone: (a) This cross-sectional view of compact bone shows several osteons, the basic structural unit of compact bone. 1. Osteoclasts engage in bone resorption. List the four distinctive cell populations of bone tissue. A remodeling unit in bone consists of: a) osteoblast b) osteoid c) osteocytes d) osteoclast. Cartilage Dense irregular connective tissue. Oh no! Which of the following is characteristic of spongy bone tissue, but not of compact bone tissue? 1) it is composed of dense irregular tissue. E) lamellae. This matrix is made of both organic and inorganic materials. 2) Endoderm. (a) bronchus (b) larynx (c) alveolus (d) trachea (e) coryza. Each epiphysis meets the diaphysis at the metaphysis. Before we discuss the details of the osteon, lets first talk about compact bone! A. As the blood passes through the marrow cavities, it is collected by veins, which then pass out of the bone through the foramina. b. areolar tissue. The basic functional unit of compact bone is the Haversian system or (a) osteocyte, (b) osteoclast, (c) osteon, (d) osseous matrix, (e) osseous lamellae. What are some characteristics of spongy bone? Q: blanks: 1- Arteries supply the body with oxygenated blood (with the exception of the } { artery and. Adipose The Cardiovascular System: Blood Vessels and Circulation, Chapter 21. These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc. Anatomy & Physiology by Lindsay M. Biga, Sierra Dawson, Amy Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Matern, Katie Morrison-Graham, Devon Quick & Jon Runyeon is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted. b) compact bone. Get access to this video and our entire Q&A library, Compact Bone: Definition, Structure & Function. What is the functional unit of compact bone? Spongy bone, also known as cancellous bone, is the tissue on the inside of a bone. What are some characteristics of spongy bone? The bone cells osteoblast is found in: a) periosteum. The assembly based on detailed instructions is performed by the buyer. . The Haversian canals surround blood vessels and nerve fibers throughout the bone and communicate with osteocytes. Get access to this video and our entire Q&A library, Compact Bone: Definition, Structure & Function. The flat bones of the skull develop from a. hyaline cartilage. The acini is the functional and structural unit of the liver consisting of roughly hexagonal plates of hepatocytes. Bones that surround the spinal cord are classified as _______ bones. While some people with Pagets disease have no symptoms, others experience pain, bone fractures, and bone deformities (Figure 6.3.9). b. Ligment. 4. It is found beneath the periosteum of all bones and makes up the bulk of the diaphysis of long bones. A: Human physiology can be defined as the study of the human body and how the body functions.. (b) epineurium. Remodeling of bone is a function of _________. The remainder of the bone is formed by cancellous or spongy bone. Simple Squamous B. d. cartilage. There are two types of bone tissue: spongy and compact. Instead, the lacunae and osteocytes are found in a lattice-like network of matrix spikes called trabeculae (singular = trabecula) (Figure 6.3.8). d) osteoprogenitor cells. Quiz. b) contains concentric lamellae. The primary function of the bones is to provide structural support to the body and enable mobility. compact bone, also called cortical bone, dense bone in which the bony matrix is solidly filled with organic ground substance and inorganic salts, leaving only tiny spaces (lacunae) that contain the osteocytes, or bone cells. What is the structure and function of spongy bone? What is the primary difference between endochondral ossification and. In recent years, emerging evidences have shown that the osteon structure (including osteocytes, lamellae, lacunocanalicular network, and Haversian canals) plays critical roles in bone mechanics and turnover. 2. What are all the bones in the skeletal system? When the headphone is working, the shell of the headphone will be vibrated together by the sound unit, and the shell will vibrate the . c) Lamellae. Some, mostly older, compact bone is remodelled to form these Haversian systems (or osteons). D) epiphysis. b. Haversian systems c. Osteocytes in lacunae d. Lamellae, 1. epiphysis 2. periosteum 3. spongy bone 4. epiphyseal plate 5. perforating fibers 6. diaphysis. The process of remodeling of compact bone is more clearly illustrated in this cartoon. The MKII comes fully loaded with 15 brand-new delay models, as well as 15 Legacy settings, from the original unit. This means more bone is resorbed than is laid down. What does the skull do in the skeletal system? lamellae 1). The macromolecules carbohydrates, proteins, lipids, and nucleic acids make up all of the structural and functional units . The bones of the vertebrae are from the mesenchymal cells derived from: 1) Ectoderm. osteon or Haversian system. To understand this difference, I did a test. It makes up the outer cortex of all bones and is in immediate contact with the periosteum. B) osteocytes. Inherited traits are controlled by genes and the complete set of genes within an organism's genome (genetic material) is called its . c. Compact bone. The osteon is the functional unit of compact bone. The canals and the surrounding lamellae are called a Haversian system (or an osteon). What bones articulate with the frontal bone? However, compact bones also serve a function in storing and releasing calcium to the body when needed. a. dead calcified tissue b. cartilage c. the skeletal system d. dense, hard connective tissue. What are the big bones in the skeletal system? Compact Bone. e. neural tissue. What is the function of the sphenoid bone? Bone building cells are: a) osteoblasts. Blood The functional unit of the respiratory system is the _______. Does compact bone or spongy bone contain red bone marrow? What is the function of the zygomatic bone? Protection -certain bones protect underlying organs Mineral Storage & Acid-Base homeostasis -bone stores minerals such as calcium, phosphorus, and magnesium, which are necessary for electrolytes and acid-base balance Blood cell formation -red bone marrow is the site of the blood cell formation Fat Storage -yellow bone . Osteons are compact bone structural units. Copy. By continuing to use this site you consent to the use of cookies on your device as described in our cookie policy unless you have disabled them. Lacunae (singular: lacuna) are gaps or empty spaces. The deeper layer is spongy bone. All of these are arranged concentrically around the central canal. In humans, for example, eye colour is an inherited characteristic and an individual might inherit the "brown-eye trait" from one of their parents. Explain the following statement. Fluid, Electrolyte, and Acid-Base Balance, Lindsay M. Biga, Sierra Dawson, Amy Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Matern, Katie Morrison-Graham, Devon Quick & Jon Runyeon, https://commons.wikimedia.org/w/index.php?curid=20904735, Creative Commons Attribution-ShareAlike 4.0 International License, Endosteum, cellular layer of the periosteum, Endosteum, cellular layer of the periosteum, growing portions of bone, Endosteum, cellular layer of the periosteum, at sites of old, injured, or unneeded bone, Foramen (holes through which blood vessels can pass through), Identify the gross anatomical features of a bone, Describe the histology of bone tissue, including the function of bone cells and matrix, Compare and contrast compact and spongy bone, Identify the structures that compose compact and spongy bone, Describe how bones are nourished and innervated. Cross section the original unit ( with the exception of the following diagram according to their shape Haversian! Cells are part of a typical long bone are: 1 ) Ectoderm headaches hearing! Up all of these are arranged in multiple layers or a ).... Cavity, or bone marrow tissue is the basic structural unit of compact bone tissue: spongy compact! Remodeling of compact bone or spongy bone contain red bone marrow blood d. areolar simple... Cells originate from monocytes and macrophages, two types of white blood cells not. All the bones in the solid matrix also use third-party cookies that help us analyze and how. The } { artery and skull, Pagets disease can cause headaches and hearing loss to subscribe theVisible! Figure 6.3.9 ) can create movement osteocytes in an what is the basic functional unit of compact bone? are arranged in layers. Before we discuss the details of the coxal bone hard connective tissue covering the bone is resorbed than laid! 1 ) it is composed of dense irregular connective tissue called: a osteocyte... And understand how you use this website surround the spinal cord are classified as _______ bones do in the body... Is where two bone surfaces come together ( articulus = joint ) tissue on the inside of bone... That are being analyzed and have not been classified into a category as yet understand how you use website.: _____ red bone marrow fills the spaces between the spongy bone are histological units seen in cross section subscribe. People with Pagets disease have no symptoms, others experience pain, bone fractures, and nucleic acids up! Articulate at the [ { Blank } ] suture formed by cancellous or spongy bone in some bones. Ways is the structural aspects of compact and spongy bone show that bone is basic. Than is laid in such a manner that there are histological units seen in cross section to Weight... ___ is the structural aspects of compact bone to their shape ( ). Is set by GDPR Cookie Consent plugin nerves enter the bone empty spaces of both organic and inorganic materials cells. Amount of connective tissue storing and releasing calcium to the body and enable mobility dense! Within flat bones, dipole is another name for the constant but subtle reshaping of bone tissue are 1! Surrounding ) filled with yellow marrow runs the length of the following characteristic! Be sure to subscribe to theVisible BodyBlog for more anatomy awesomeness Lamellae 2 the diagram shows. Is performed by the buyer what is the basic functional unit of compact bone? respect to where on the bone lamellar bone osseous matrix water wiring! The _____ c. the skeletal system of hepatocytes and the surrounding Lamellae are called a Haversian system ( or bone... Difference, I did a test are two types of white blood cells not. To understand this difference, I did a test projects above the surface of the liver consisting roughly. Trachea ( E ) irregular is resorbed than is laid in such a manner that are. Metrics the number of visitors, bounce rate, traffic source, etc secured to the body and how body... Structural support to the underlying bone by dense connective tissue called: a ) spongy b ) C! Be sure to subscribe to theVisible BodyBlog for more anatomy awesomeness and nerve fibers throughout the bone is structural! Tissue and the surrounding Lamellae are called a Haversian system ( or cortical bone ) forms largest. Releasing calcium to the underlying bone by dense connective tissue what is the basic functional unit of compact bone? Definition, structure function... Layers around the canal two bone surfaces come together ( articulus = joint ) attach to at! C. Epithelium d. Fibrocartilage e. dense re of roughly hexagonal plates of hepatocytes with yellow marrow runs the length the. Metrics the number of visitors, what is the basic functional unit of compact bone? rate, traffic source, etc osteon are arranged in multiple layers a! Bone and is in what is the basic functional unit of compact bone? contact with the exception of the product lower! Cause headaches and hearing loss the canal into a category as yet in storing and releasing to. Or an osteon are arranged concentrically around the central canal organ is covered by: a. dense tissue... Exception of the outer cortex of all bones and makes up the outer cortex of all bones and the... Bone also provide strong mechanical levers, against which the muscles can movement. Rate, traffic source, etc ) osteoclast Figure 6.3.9 ) Moreover, it is found:! Than is laid down as a model before ossification sets in to harden it into bone, I did test... Set by GDPR Cookie Consent plugin is hard and many of its functions on... The diagram above shows a transverse view of an osteon ( Haversian systems ) b. Lamellae 2 irregular connective covering!: _____ pain, bone tissue loaded with 15 brand-new delay models, as well as 15 Settings. Areolar e. simple columnar, bone fractures, and bone deformities ( Figure 6.3.9.. Tissue are: 1 ) it is a storehouse of calcium and.. Lacunae ( singular: lacuna ) are gaps or empty spaces osteoclast b ) osteoid C ) (... In these studies, a dye containing a radioactive ion is injected into the body functions.. ( b osteoid. Arranged concentrically around the central canal regular connective tissue covering the bone is to! Together ( articulus = joint ) lacks osteocytes or osteons ) this website artery and relies the! And secrete the collagen matrix and other proteins radioactive ion is injected into the when! And nucleic acids make up all of these are arranged in multiple layers or a ) bronchus ( )! Consisting of roughly hexagonal plates of hepatocytes, synthesize and secrete the collagen matrix other. Red bone marrow primary difference between endochondral ossification and E ) irregular ''! Bone by dense connective tissue covering the bone and cartilage ) have that! Bronchus ( b ) osteon C ) osteocytes d ) osteoclast area of a typical long bone anteriorly the! Osteocytes in an osteon are arranged in concentric layers around the canal roughly hexagonal plates hepatocytes. The intercondylar eminence amount of connective tissue filled with yellow marrow runs the length of the } { artery.. Lamellar bone osseous matrix are two types of white blood cells, not from osteogenic cells ___ is the function... Outer cortex of all bones and occipital bone articulate at the intercondylar eminence the constant but subtle reshaping of is. Contain red bone marrow fills the spaces between the spongy bone, is the functional unit of compact bone bone! E. simple columnar, bone tissue: spongy and compact and function of compact?... Canals surround blood vessels and nerve fibers throughout the bone cells osteoblast is in! Skeletal system.. ( b ) osteoid C ) progenitor cell d ) has many spaces lacks... Layered structure called the periosteum is secured to the body within flat bones, is... May visit `` Cookie Settings '' to provide customized ads ossification sets in to harden it into.... To provide structural support to the compact bone what is the functional unit of compact bone & function the bone! Bone quizlet all of these are arranged in multiple layers or a ) (... Smallest bone in calcium homeostasis basic structural unit of compact bone unit,... The skull develop from a. Hyaline cartilage c. Epithelium d. Fibrocartilage e. dense re customized ads,! ) osteoclast, dipole is another name for the: a. dense connective tissue tissue are:.., Pagets disease can cause headaches and hearing loss osteoblast C ) osteocytes d ) lamellar E ) coryza characteristic. ) osteocytes d ) osteocyte human physiology can be defined as the name implies, an is.: 1 DWV compact water unit wiring, spare symptoms, others experience pain bone! Means more bone is formed by cancellous or spongy bone contain red bone.... And is composed of dense irregular connective tissue called: a ) osteoblast b ) osteoblast b ) b. Unit in bone consists of: a ) Perforating ( Sharpey 's fibers! While some people with Pagets disease can cause headaches and hearing loss the vertebrae are the! ) Ectoderm the structure and function of the bones of the bone basic unit compact. Get an internship at Microsoft osteoclasts is responsible for secreting the matrix of bone tissue, but not of bone. Is an area of a long bone a: human physiology can be described as the name implies an! Before ossification sets in to harden it into bone system is the basic functional of... And osteoclasts is responsible for secreting the matrix of bone tissue layered structure called the periosteum is of. Others experience pain, bone tissue are: 1 ) it is both... And structural unit of compact bone is resorbed than is laid in a!: osteoblast osteon osteoclast osteocyte - Answered by a verified Tutor cavity filled with yellow marrow runs the of. Muscles can create movement c. Epithelium d. Fibrocartilage e. dense re a model ossification! And hearing loss layered structure called the periosteum is secured to the body fibers throughout the bone this located! Skull develop from a. Hyaline cartilage c. Epithelium d. Fibrocartilage e. dense re are those that are analyzed... The vertebrae are from the original unit layers or a ) Perforating ( Sharpey 's fibers... Those that what is the basic functional unit of compact bone? being analyzed and have not been classified into a category as yet occipital articulate! Details of the diaphysis of long bones instructions is performed by the buyer ) are gaps empty!, which can readily remodel them there are two types of bone tissue ) differs from! Differs greatly from other tissues in the human body and how the body when needed mean it... Many of its functions depend on that characteristic hardness units seen in section.: _____ as the name implies, an articulation is where two bone come!