The skeleton¹ is the inner framework of bones that supports and gives shape to the human body.It also protects some of the soft organs of the body -- the skull² surrounds the brain， for example. Muscles and ligaments³ pull on the bones of the skeleton at joints to make the body move.

Weight for weight，bone is five times stronger than steel， but it is very light. The skeleton makes up only one- sixth of an adult's weight.The skull in particular is very strong，because it has to protect the brain and sense organs， such as the eyes， ears and nose.

This strong yet flexible material is a living tissue， made up of bone cells embedded⁴ in a matrix⁵ of fibers. Bone is not solidblood vessels⁶ and nerves run through tunnels within it， and some areas are a honeycomb⁷ of small spaces.In the center of many bones is a cavity⁸ packed with a jellylike⁹ substance called bone marrow¹⁰.

Bones connect at joints. Different types of joints allow different movements. Joints are often held together by strapsil of tough fibrous tissue， called ligaments， and the muscles that cross the joint.

注釋：

1．skeletonn. 骨骼，骨架

2．skull n．顱骨，頭骨

3. ligament n．韌帶

4．embedvi．嵌入

5．matrixn．[生]基質(zhì)

6．vessel n．[解)血管，脈管

7．honeycomb n．蜂巢狀的東西

8．cavityn．[解]腔，窩

9．jellylikeadj．像膠凍的，像膠狀物的

10．marrown．髓，骨髓

11．strap n．帶，帶條，布帶

骨架是骨骼的內(nèi)部結(jié)構(gòu)，支持并構(gòu)成人體的輪廓。它也保護身體內(nèi)一些柔軟的器官，例如環(huán)繞大腦的顱骨。肌肉和韌帶在關(guān)節(jié)處拉動骨架中的骨骼以使身體運動。

相同重量的骨骼比鋼鐵結(jié)實5倍，但是骨骼非常輕。骨架只占一個成年人體重的六分之一。尤其是顱骨非常結(jié)實，因為它需要保護大腦和感覺器官，比如眼睛、耳朵和鼻子。

骨骼這種結(jié)實且柔韌的物質(zhì)是一種生物組織，由嵌在纖維基質(zhì)中的骨細胞組成。骨骼不是實心的——血管和神經(jīng)貫穿它內(nèi)部的通道，一些地方則是具有小空間的蜂窩狀結(jié)構(gòu)。許多骨骼的中央有一個空腔，其中充滿著一種叫做骨髓的膠狀物質(zhì)。

骨骼在關(guān)節(jié)處連接，不同類型的關(guān)節(jié)適于不同的運動。關(guān)節(jié)由幾條叫做韌帶的堅韌的纖維組織以及跨過關(guān)節(jié)的肌肉結(jié)合在一起。