SOME OBSERVATIONS ON THE PYRAMIDALIS MUSCLE
- VernacularTitle:关于锥状肌的一些观察
- Author:
Chun CHANG
- Publication Type:Journal Article
- From:
Acta Anatomica Sinica
1955;0(03):-
- CountryChina
- Language:Chinese
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Abstract:
The pyramidalis muscle is one ef the muscles in the body whose nature and function remain unknown. Some authors consider it to be a vestigial muscle phylogenetically derived from monotremes in which it is highly developed, but others believe it to be a newly formed structure in the primate, reaching its highest development in man. Among the human races, the white race is reported to have greater percentage of absence (17.7%) than in the black and yellow races. Some authors hesitate to accept the progressive muscle theory due to racial prejudice. For the Chinese, only 40 bodies have been studied and the percentage of absence is only 1.25%. In order to re-estimate the frequency of absence of this muscle in the Chinese and to seek for evidences that might throw light on the nature of this muscle, 112 children of different ages and 10 adults have been studied. In the children this muscle grows twice in length and width from the time of birth to early adolescence (body ength 130 cm), since then no further development is observed. The perc- entage of absence, in this group, is 5.7% in term of side which is slightly higher than that of the Japanese but is still much lower than the other races. It was found that some muscle fibers of the m. rectus abdominis may arise from the linea alba directly opposite the insertion of the pyramid alis muscle. The occurrence of such fibers leads one to consider that they, together with the pyramidalis muscle, may be able to draw the lower abdominal wall inward which tends to bulge in an upright position at the time of increased abdominal pressure. This tends to direct the abdominal pressure towards the pelvic cavity, facilitating the evacuation of the content of the pelvic viscerae. Since this condition develops as a sequence of the upright position in the human bcdy, it should be progressive in nature. It has also been observed that the pyramidalis muscle is enclosed in a special sheath formed by the aponeurosis of the united lower portion of the m. obliquus internus abdominis and m. transversus abdominis. The relation of this muscle with the aponeurosis of the internal oblique muscle and the continuance of this muscle with the rectus abdominis at the linea alba suggest its origin from the rectus muscle.
