Anatomy Atlases: Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: S: Serratus Posterior Inferior and Serratus Posterior Superior

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Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: S

Serratus Posterior Inferior and Serratus Posterior Superior

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed

There is considerable variation in the number of digitations of these muscles. The number of slips of the serratus superior may be reduced to five or six slips. Mori (1964) describes the vertebral origin of serratus posterior superior, in his cases, as follows:

Cervical	Thoracic	Right side	Left side	Total	%
IV - VII		2	2	4	4
V - VII		5	7	12	12
VI	I	18	15	33	33
V	I	20	21	41	41
VI	I	2	1	3	3
IV	II	1	2	2	2
V	II	2	2	4	4

Upper Limit

Cervical	Right side	Left side	Total	%
IV	24	18	42	42
V	27	30	57	57
VI	2	1	3	3

Lower Limit

Cervical/ Thoracic	Right side	Left side	Total	%
VII	7	9	16	16
I	40	37	77	77
II	3	3	6	6

Insertion

(From Mori, 1964)
The ribs of insertion are as follows:

Ribs	Right side	Left side	Total	%
II, III, IV	44	40	84	26
II, III, IV, V	72	76	148	46
II, III, IV, V, Vi	10	6	16	5
III, IV	4	0	4	1
III, IV, V	34	38	72	23

The serratus inferior may be reduced to two digitations, the first and last being absent.

Upper Limit of Vertebral Origin of Serratus Posterior Inferior

(From Mori, 1964)

Upper Limit	Right side	Left side	Total	%
T X	15	16	31	31
XI	31	29	60	60
XII	4	3	7	7
L I	0	1	1	1
II	0	1	1	1

Insertion

Ribs	Right side	Left side	Total	%
VIII, IX, X,XI, XII	3	2	5	2.1
IX, X, XI	22	22	44	11.5
X, XI	3	4	7	2.0
X, XI, XII	3	3	6	1.5
Xi, XII	2	1	3	1.0

The 11th rib is the lowest limit of insertion in 61 sides, 26% and the 12th rib is the lowest limit of insertion in 145 sides, 93% of Mori's cases.

Absence of the superior and inferior muscles have been recorded but this is extremely rare; when absent they are replaced by fibrous tissue. Cases have been described, in which the serratus inferior showed irregular arrangements of its digitations as a result of associated accessory muscles.

Syn.: mm. (serrati posterior) Hintere Sägemuskeln, Petits dentelés postérieurs.

References

Anson, B.J., Ed. (1966) Morris' Human Anatomy, 12th ed. The Blakiston Division, McGraw -Hill Book Company, New York.

Macalister, A. (1875) Additional observations on muscular anomalies in human anatomy (third series), with a catalogue of the principal muscular variations hitherto published. Trans. Roy. Irish Acad. Sci. 25:1-134.

Mori, M. (1964) Statistics on the musculature of the Japanese. Okajimas Fol. Anat. Jap. 40:195-300.

Williams, P.L., Warwick, R., Dyson, M. and L.H. Bannister., Eds. (1989) Gray's Anatomy, 37th ed., Churchill Livingstone, Edinburgh.

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