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Chapter: BIOLOGY (ZOOLOGY) Standard XI first year 11th text book Assignment topics question and answer Explanation Definition

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Structure of a typical long bone

Structure of a typical long bone
A bone is covered by a double layered sheath called the periosteum. The outer layer of the periosteum is fibrous in nature. It is a dense collag-enous layer having blood vessels and nerves.

Structure of a typical long bone

 

A bone is covered by a double layered sheath called the periosteum. The outer layer of the periosteum is fibrous in nature. It is a dense collag-enous layer having blood vessels and nerves.

 

A growing long bone has three regions. The long bony part is the dia-physis or shaft. It is made up of compact bone.

The end of the bone consists of epiphysis. It is made up of spongy bone. The outer surface of epiphysis is formed of compact bone. In between the epiphysis and diaphysis epiphyseal or growth plate is found. It is made up of hyaline cartilage. Growth in length of bone occurs at this plate.

 

The cavity inside the diaphysis is called the medullary cavity. This cavity is lined by a membrane called the endosteum. The cavity inside the diaphysis in adults contain yellow marrow. It is mostly adipose tissue. The medullary cavity of the epiphysis contains red marrow concerned with blood cell formation.

 

Dried, prepared bones are used to study skeletal anatomy. The bones are named according to their position in the body. The named bones are di-vided into two categories: (1) the axial skeleton and (2) the appendicular skeleton. The axial skeleton consists of the skull, hyoid bone, vertebral col-umn and thoracic cage. The appendicular skeleton consists of the limbs and their girdles. In human body, there are 206 bones, of these 80 are in the axialskeleton, 126 in the appendicular skeleton. Among the bones of the axial skeleton 28 bones are in the skull26 bones in the vertebral column25 bones in the thoracic cage and one remains as the hyoid bone. (details as found below)


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