Classica Sinica Medica

尾骶

wěi dǐ

The tail bone · wei di

Also rendered: Tail bone (plain, and it keeps 尾) · Sacrum (the modern name) · Sacrococcyx (precise, and it is later anatomy)

Physiology

Reviewed · 2026-10-24

At a glance

Pinyin
wěi dǐ
Simplified
尾骶
Literal
尾 wěi — tail; 骶 dǐ — the bone at the base of the spine, written with the bone radical over 氐, the root. The pair names the end of the spinal column, counted here as the terminus of twenty-one vertebrae.
Shuowen
《說文》無骶字，从骨从氐，氐亦聲，蓋後起。「尾骶」本篇1見，為脊骨二十一節之末：膂骨以下至尾骶二十一節，長三尺。

In brief

The lower end of the spine, given as the terminus of a count rather than a shape. From the spinal bone down to it there are twenty-one vertebrae and three chi. The chapter then divides that length: the upper vertebra is one cun and a fraction of four, the odd fraction falls to the lower ones, and the upper seven come to nine cun and seven eighths. It is the only place in the book where the spine is both counted and measured.

Senses in the classical corpus

1
The terminus 膂骨以下至尾骶二十一節
膂骨以下到尾骶共二十一节
From the spinal bone to the sacrum are twenty-one vertebrae.
膂骨以下至尾骶二十一節 — 靈樞·骨度

Occurrences in the classics

Passages where the term does real work, with the original, pinyin and English on the same line.

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1 passages
靈樞·骨度 Read in context →
項髮以下至背骨長二寸半。膂骨以下至尾骶二十一節，長三尺。上節長一寸四分分之一，奇分在下，故上七節至于膂骨九寸八分分之七。此衆人骨之度也，所以立經脉之長短也。是故視其經脉之在于身也，其見浮而堅，其見眀而大者，多血；細而沉者，多氣也。 项发以下至背骨长二寸半。膂骨以下至尾骶二十一节，长三尺。上节长一寸四分分之一，奇分在下，故上七节至于膂骨九寸八分分之七。此众人骨之度也，所以立经脉之长短也。是故视其经脉之在于身也，其见浮而坚，其见眀而大者，多血；细而沉者，多气也。
xiàng fà yǐ xià zhì bèi gǔ cháng èr cùn bàn. lǚ gǔ yǐ xià zhì wěi dǐ èr shí yī jié, cháng sān chǐ. shàng jié cháng yī cùn sì fēn fēn zhī yī, qí fēn zài xià, gù shàng qī jié zhì yú lǚ gǔ jiǔ cùn bā fēn fēn zhī qī. cǐ zhòng rén gǔ zhī dù yě, suǒ yǐ lì jīng mài zhī cháng duǎn yě. shì gù shì qí jīng mài zhī zài yú shēn yě, qí xiàn fú ér jiān, qí xiàn míng ér dà zhě, duō xuè; xì ér chén zhě, duō qì yě.
From the hairline at the nape down to the spinal bone is two cun and a half. From the spinal bone down to the sacrum there are twenty-one vertebrae, three chi long. The upper vertebra is one cun and a fraction of four; the odd fraction lies below, so the upper seven vertebrae down to the spinal bone come to nine cun and seven eighths. This is the bone measure of an ordinary man, and it is what the length of the channels is based on. Hence when one looks at the channels in the body, those that appear floating and hard, or bright and large, have much blood; those fine and deep have much qi.
「尾骶」本篇1見，與「膂骨」對舉，為脊骨二十一節之首尾。

Compounds built on this term

尾骶
wěi dǐ
the tail bone
脊骨末節
膂骨
lǚ gǔ
the spinal bone
脊骨

How it has been translated

Every rendering below is a decision about which reader is being addressed. There is no neutral option.

This sitethe sacrumfamiliar, and it names the region
Literaltail bottom-boneexact, and it is not English
Clinicalthe sacrococcygeal endclear, and it is modern

Entry status

Review pending — who reviews this?

2026-10-24

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Reading path

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