Both atria are thinwalled muscular chambers.是什么意思？

Both atria are thinwalled muscular chambers.

两心房是由薄壁构成的空腔.

both

adj. 二者，两者都；pron. 二者；adv. 二者，二者都；conj. 不仅…而且…，…和…都；

例句
The gym can be used by both able-bodied and disabled people.
这家健身房健全和残障人士都可使用。

Atria

n. 心房，心耳，内耳窝，（古罗马建筑的）前室；

例句
Both atria are thinwalled muscular chambers.
两心房是由薄壁构成的空腔.

are

vi. （用于第二人称单复数现在时，第一、三人称复数现在时）是；n. 公亩（等于100平方米）；

例句
We are scared to abandon ourselves to our feelings in case we seem weak or out of control.
我们不敢放纵自己的情感，以免显得太过软弱或缺乏自制。

muscular

adj. 肌肉的，壮健的，肌肉发达的，强壮的；

例句
In China Grace Thompson observed the great variety of loads that were carried by 'slim, erect but muscular Amazons'.
在中国，格雷丝·汤普森看见“苗条、挺直而强健的女人们”携带着各种物品。

Chambers

n. 房间( chamber的名词复数 )，（议会的）议院，卧室，会议厅；

例句
...the rock from which the lower chambers and subterranean passageways have been hewn.
开凿出下闸室和地下通道的岩石