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The relation of the sciatic nerve to the piriformis muscle in American whites and negroes.

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THE RELATION O F THE SCIATIC NERVE TO THE
PIRIFORMIS MUSCLE I N AMERICAN
WHITES AND NEGROES1
MILDRED TROTTER
Department of Anatomy, Washington University, St. Louis, Missouri
I n the majority of cases the relation of the sciatic nerve to
the piriformis muscle is a deep one, the nerve lying ventral
to the muscle and emerging from its inferior border to continue distalward. Variations from this relationship are
chiefly the partial or complete division of the muscle by a
part or the whole of the nerve. These variations have been
noted by many anatomists and the incidence is usually found
to be between 10 per cent and 20 per cent; e.g., Eider, 18 per
cent ; Paterson, 13 per cent ; LeDouble, 17 per cent ; Bardeen
and Elting, 10 per cent. These reports have all been based
on whites except for that by Bardeen and Elting. Their
observations from the Anatomical Laboratory of Johns
Hopkins University were made on dissecting-room material
composed of both white and negro bodies-material quite
similar to that of this laboratory. They found that “neither
sex, race, side of body nor skeletal conditions seemed to have
intimate association with the natural separation of the sciatic
nerve. ’’
The dissecting-room material in this laboratory affords an
opportunity to compare further the incidence of variation of
the relations of these structures in whites and negroes. Both
the nerve and muscle are large enough to eliminate the possibility of destruction during routine dissection. With the
cooperation of the students, records of this relationship in
‘Aid in helping to carry out this research was received from the Rockefeller
Research Fund.
321
322
MILDRED TROTTER
the cadavers have been kept for the past six years. A summary of the incidence of variations in the relative positions
of the nerve and muscle is given in the table; differences
between race, sex, and side of the body are included.
The incidence of bilateral and unilateral variation is approximately the same. However, unilateral variation occurs
TABLE 1
Variation f r o m the usual relationship between the sciatic n e r m and the piriformis
muscle in cadavers with reference t o race, sex, and side of body
SIDES
BODIES
KACE
SEX
__-
White Male
Negro Male
White Female
Yumher
Per
cent
Incidence
Both sides only, 11
Right only,
5
102 Left only,
6
Total bodies, 2 22
____ ~
_
Both sides only, 6
Right only,
31
8 1 Left only,
5
-I
5
17
Total bodies,
.~
Both sides only, 1
Right only,
0
204
-~
162
-
~
30
IBoth sides only, 3
Right only,
1
2
34 Left only,
Negro Female
-.
Total
bodies,
6 18
~.
-__
Total
%-:
__,__--
Both sides only, 21
Right only,
9
232 Left only,
33
Total bodies,
19
68
1
Per
cent
Incidence
~
Both sides only, 22
Right only,
5
Left only,
6
Total sides, 33 16
_ _ _ ~ _ _
Both sides only, 12
Right only,
3
5
Left only,
Total sides, 201 12
~ _ _ _
-21
Both sides only,
Right only,
0
0
Left only,
Total sides,
2
7
- -1
'Both sides only, 61
Right only,
1
2
Left only,
~
~
-~
Total sides,
9 13
_ Both sides only, 42
Right only,
9
13
464 Left only,
__
Total sides, 64 14
_
slightly more often on the left side than on the right in all
the groups except the white female group, which is too small
for statistical comparisons. The number in this group is
inadequate also for a racial comparison of females. A comparison between whites and negroes in the male group shows
the whites to be somewhat more variable than the negroes.
This is interesting because of the assertion of Rosenmiiller,
~
RELATION OF SCIATIC NERVE AND PIRIFORMIS MUSCLE
323
questioned by both Testut and LeDouble, that a premature
bifurcation of the sciatic nerve (which almost invariably is
the case in an altered relationship of the nerve and the piriformis muscle) occurs more often in northern races than
in meridional (southern) races.
The findings on this material (excluding the white female
group which is too small for comparison) may be summarized
as follows: the whites are more variable than the negroes;
no sex difference is present in the negroes; and the left side
is very slightly, but consistently, more variable than the right.
LITERATURE CITED
EISLER,P. 1892 Der Plexus lumbo-sacralis des Menschen. Halle.
PATERSON,
A. M. 1894 The origin and distribution of the nerves to the lower
limb. J. Anat. and Phys., vol. 28, pp. 84-95.
BARDEEN,
C. R., AND ELTING,
A. W. 1901 A statistical study of the variations
i n the formation and position of the lumbo-sacral plexus in man,
p a r t 11. Anat. Anz., Bd. 19, S. 209-239.
LEDOUBLX,A.-F. 1897 Trait6 des variations du systhne musculaire de 1’homme,
T. 2. Paris.
TESTTJT, L. 1884 Les anomalies musculaires chez l’homme. Paris.
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sciatic, muscle, piriformis, relations, nerve, white, american, negroes
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