Extremely few studies have been published on the site of belly of thigh muscles. In our studies, 41 specimens (from 27 male and 14 female subjects) for anatomical investigation were used to examine the site of belly, which had often been employed for surface electromyogram. Not to say, “the belly of muscle” means the site showing the maximal value of circumference of each muscle.
The results were as follows.
1) Using nine thigh muscles, the full length of each muscle and the distance from the origin to the belly were directly measured at the first steps in the present study. Ratio of the distance from the origin to the full length was calculated. The ratio, as the average of all subjects, was 24.4% for M. sartorius, 30.8% for M. rectus femoris, 59.2% for M, vastus medialis, and 32.8% for M. vastus lateralis in the frontal aspect of thigh; 15.2% for M. gracilis, 67.9% for M. adductor longus in the inner aspect of thigh; and 44.1% for M. biceps femoris (caput longum), 29.3% for M. semitendinosus, and 65.5% for M, semimembranosus in the posterior aspect of thigh. However, no significant difference was found between the sex as well as age in the value of ratio.
2) Secondarily, “the cross section method” in this paper was used to evaluate the site of belly and measure the size of cross sections of M. sartorius and M, rectus femoris. The values were obtained from 3 specimens. The belly of M. sartorius was found at the site of 29% from the origin and that of M. rectus femoris was at 33%. The size of each cross sections was 1.3cm² and 3.5cm² respectively.
3) In addition, computed tomography was employed for 5 male adults to find the site of belly of M, sartorius and M. rectus femoris. The results were compared with those of specimens mentioned in 2) . The findings from the computed tomography showed the belly at the site of 25-29% from the origin for M, sartorius and 29-33% for M. rectus femoris. The size of cross sections of each muscle measured 2.9cm² and 11.4cm² respectively. These sites were confirmed to be coincided with those of anatomical specimens.
4) It can be, therefore, concluded that the values obtained from the direct method are applicable to those of living persons.

Study on the sites of nerve entrance in innervation of skeletal muscles is important in the field of anatomy, histology, physiology and pathology, and since 19 th century, many researchers have been engaged in the macroscopical investigations on nerve entrance of muscles. However, their results were not always precise, because they seemed to employ macroscopical methods without measuring a length of muscles and a distance between origin and insertion of various muscles in thigh
In this paper, first, the muscle length was determined by measuring the distance between origin and insertion directly (designated here as“direct method”) or by measuring the length of muscles along their course (designated here as“indirect method”) by scale. Concomitantly, the number and diameter of major innervated nerves of each muscle were also examined. Next, the distance between nerve entrance and the origin of 9 thigh muscles were carefully measured. The difference of the values obtained referring to sex and age was also surveyed. Adding to it, the correlation between the sites of nerve entrance and that of muscle belly was also studied. The details of respite were ae fn11imr
1) The values of muscle length obtained from direct and indirect methods were compared in paying attention to each belly of muscles. 10 specimens in M, sartorius and M, rectus femoris were used for it. The difference of values between direct and indirect methods was negligible, that is, only 1 to 2.5% difference are there respectively.
2) The number of major nerve entering into each muscle were one or two. The number of major nerves and their diameter (parenthesized) of 21 specimens were as follow; one (1.6 mm) for M, sartorius, two (1.6 mm) for M. rectus femoris, two (2.4 mm) for M, vastus medialis and M. vastus lateralis, one (1.8 mm) for M, gracilis, one (1.7 mm) for M. adductor longus, two (2.4 mm) for M, biceps femoris (caput longum), two (2.5 mm) for M, semitendinosus and two (2.6 mm) for M, semimembranosus.
3) Using 41 specimens, the sites of nerve entrance where one or two major nerves were entered into thigh muscles were measured with the indirect methods. The sites of nerve entrance were indicated with the ratio calculated from the formula described in Result-C. Their sites were 21.4% from the origin for M, sartorius, 14.9% and 25.5% for M. rectus femoris, 22.6% and 39.3% for M. vastus medialis, 17.0% and 35.1% for M, vastus lateralis, 22.3% for M, gracilis, 44.7% for M, adductor longus, 22.1% and 38.6% for M. biceps femoris (caput longum), 15.5% and 43.0% for M. semitendinosus, and 46.7% and 61.7% for M, semimembranosus. However, the difference in the sites of nerve entrance related to sex and age was hardly in those specimens.
4) The difference between the sites of nerve entrance (either one or two) and muscle belly was evident in M, vastus medialis and M, adductor longus. The values of deviation in M. vastus medialis and M. adductor longus stood about at 20%. The difference of the other muscles (M. sartorius, M, rectus femoris, M, vastus lateralis, M, gracilis, M, biceps femoris; caput longum, M, semitendinosus, M, semimembranosus) stood at 3 to 7%.
5) Some discussions were devoted to the relationship of sites between nerve entrance in anatomy and motor point in kinesiology.