Statistical Observations on the Musculi Interspinales of the Japanese

Okajimas Fol. anat. jap., 53 : 231-244, 1976

Ryosuke Miyauchi

Department of Anatomy, School of Medicine, Fukuoka University, Fukuoka 814, Japan

-Received for Publication, March 15, 1976-

Introduction The Mm. interspinales of man have been studied by Eisler (1912) and Virchow (1914-a) for Europeans, by Loth (1912) and Lanz (1922) for negroes, by Nishi (1921) for the Japanese, by Kurz (1922) for Chinese newborn and by Shindo (1930) for the Ainu, but all of these reports were based upon a small number of cases except for the study by Nishi. In the report of Nishi (1921), the Mm. dorsi proprii of a total of 100 sides of 50 Japanese were examined and the results were processed statistically. However, a description of the Mm. interspinales was made for only the cervical region in his report with no mention of these muscles in the thoracic, lumbar or sacral region. Conclusions based upon the examination of a few cases are inevita- bly accompanied by errors due to the influence of variations and indi- vidual differences. It is believed that as many cases as possible should be examined and the results are processed statistically in order to avoid this difficulty and determine the normal condition. Because of the aforementioned situation, the present study was made from the above standpoint to determine the normal condition of the Mm. interspinales of the Japanese and it is hoped that the results will serve to supplement the reports of these earlier investigators. During the examinations in this study, fine muscle bundles were found extending between adjacent tendons of insertion of the M. semispinalis cervicis or between the tendon of insertion of the M. semispinalis cervicis and the spinous process of the cervical vertebra. Al- though they were adhered to some degree with the Mm. interspinales cervicales, it was felt that these muscle bundles correspond to the so- called Fasciculi intertendinosi of Virchow (1907). A description of these muscle bundles will not be made in the present paper.

231 232 Ryosuke Miyauchi

Material and Method The material consisted of 60 sides of 30 bodies (15 males and 15 females) selected at random from among the material used for training in anatomical dissection at the School of Medicine, Fukuoka University in 1974 (52 bodies) and 1975 (48 bodies) (total 100 bodies). All of these bodies had been fixed by the injection of a mixture of 10% formalin and 80% alcohol into the femoral artery. This study was made during the course of training of medical students in the practice of anatomical dissection. Inspection of the Mm. interspinales had been made prior to dissection of these muscles by the medical students. Examinations were made using dissection tweezers and a scapel under the magnifying lens equipped with an illumination attachment.

Findings and Discussion The Mm. interspinales, located the most medially among the Mm. dorsi profundi, are muscles that connect adjacent spinous processes and are present in the area below the 2nd cervical vertebra. For the sake of convenience, these muscles were separated into the Mm. interspinales cervicales, the Mm. interspinales thoracales, the Mm. interspinales lumbales and the M. interspinalis sacralis according to the method of Eisler (1912) and Shindo (1930). Furthermore, the Mm. interspinales cervicales were subdivided into the M. interspinalis cervicalis longus (the so-called M. spinalis cervicis) which connects the spinous processes with at least one spinous process interposed between the origin and insertion, and the Mm. interspinales cervicales (breves) which connect adjacent spinous processes in the cervical region. Concerning the intrinsic nature of the M. interspinalis cervicalis longus, there is disagreement on whether this muscle should be included in the Interspinalis system or the Spinalis system. Virchow (1907, 1914-a, 1914-b, 1916), Nishi (1938), Ura (1970), Mori et al. (1970), etc. claim that the muscle described heretofore by the name of the M. spinalis cervicis should be included in the Interspinalis system as actually being the M. interspinalis cervicalis longus. In contrast to this, the previous study by this author had yielded findings that showed this muscle to be innervated by a branch from the same nerve system as that which supplied the M. semispinalis cervicis so that it had been concluded that this muscle was the genuine M. spinalis cervicis. Some room for question remained, however, concerning the constancy of this muscle in each case, and it seems that it can not yet necessarily be concluded that there is no possibility for this muscle to be innervated by a branch from the same nerve system as that which supplies the Statistical Observations on the Musculi Interspinales of the Japanese 233

Mm. interspinales (Miyauchi, 1975-a, 1975-b). The purpose of the present study, however, is the determination of the normal condition of the Mm. interspinales of the Japanese through statistical observations. Therefore, the muscle which is located near the ligamentum nuchae in the cervical region and connects the spinous processes with at least one spinous process interposed between the origin and insertion, will be described collectively here as the M. interspinalis cervicalis longus (the so-called M. spinalis cervicis). The determination of its intrinsic nature will be left to future studies. Moreover, the Mm. interspinales thoracales were present only in the upper and lower thoracic regions with none in the mid-thoracic region. In view of the aforementioned situation, the muscles of the cervical region were classified into the M. interspinalis cervicalis longus (the so- called M. spinalis cervicis) and the Mm. interspinales cervicales (breves), while the muscles in the thoracic region were subdivided into the Mm. interspinales of the upper thoracic region and those of the lower thoracic region in the present paper.

1. Mm. interspinales cervicales These muscles, as mentioned earlier, were separated into the M. interspinalis cervicalis longus (the so-called M. spinalis cervicis) and the Mm. interspinales cervicales (breves). Examination of the ralationship between these muscles showed the former to be located on the dorsal side of the latter with some degree of adhesion between them at the origin and insertion.

(a) M. interspinalis cervicalis longus (the so-called M. spinalis cervicis) (figure) This muscle was absent in many cases in this study and was present at the frequency of 81.7% (49 sides out of 60 sides). The frequency of this muscle in this study is slightly higher than that reported for the Japanese (Nishi, 1921) and the Ainu (Shindo, 1930), but the difference is not significant (Table 1). Nishi reported this muscle to be absent more frequently on the right side in the

Table 1. Frequency of the M. Table 2. Absenceof the M. inter- interspinalis cervicalis longus (the so- spinalis cervicalis longus (the so-called called M. spinalis cervicis). M. spinalis cervicis). 234 Ryosuke Miyauchi

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Japanese, whereas Shindo found it to be absent more often on the left side in the Ainu. In contrast to this, the frequency of absence of this muscle showed no difference by side in the present study (Table 2 and Figure). The level of the upper and lower limits of this muscle had been examined statistically by Nishi (1921), but the method of processing Statistical Observations on the Musculi Interspinales of the Japanese 235 the data used by Nishi is inappropriate for cases having the multiple occurrence of this muscle on one side such as in the reports by Virchow (1914-a) and Kurz (1922). Cases with multiple occurrence of this muscle on the same side such as noted by Virchow and Kurz were also found in the present examination (14 sides, 28.6%). For example, on the left side of subject number 58 there were two muscles. That is, the upper one connected the spinous process of the 6th cervical vertebra with the spinous process of the axis, while the lower muscle which arose from the spinous process of the vertebra prominens, ran upward and inserted into the spinous processes of the 3rd and 4th cervical vertebrae by two digitations, and although these digitations of insertion ran along the ventral side of the upper muscle, no adhesion was noted between the upper and lower muscles. Two muscles were noted on the same side in 13 cases in the present examination. Furthermore, 1 case showed the presence of three muscles on 1 side (subject number 68, left side). Statistical examination of the upper and lower limits of this muscle by the simple method of Nishi is not felt to be appropriate for such cases having multiple occurrence of this muscle on one side. Therefore, the level of the upper and lower limits of the location of this muscle was processed statistically in the present study. The upper limit of the location of this muscle in the present examination ranged from the axis to the 4th cervical vertebra and was most frequently at the level of the spinous process of the axis (36 sides, 73.5%). The upper limit of this muscle was also most often found to be the spinous process of the axis in the report of Nishi (1921), but at a considerably lower frequency than in the present study. The upper limit was reported to be the spinous process of the axis in the Ainu (Shindo, 1930), Europeans (Virchow, 1914-a) and Chinese newborn (Kurz, 1922) as well as in negroes (Loth, 1912 : Giacomini ; cited from Loth). Therefore, the upper limit of the location of this muscle in man may be regarded to be usually at the level of the spinous process of the axis (Table 3).

Table 3. Upper limit of the location of the M. interspinalis cervicalis longus (the so-called M. spinalis cervicis). 236 Ryosuke Miyauchi

Next, the lower limit of the location of this muscle in the present examination ranged from the 4th cervical to the 1st thoracic vertebra. It was mainly between the 5th to 7th cervical vertebra, but most frequently the lower limit was at the level of the spinous process of the 6th cervical vertebra (18 sides, 36.7%). In comparison with this, the lower limit in the Ainu (Shindo, 1930) was reported to be one vertebral body lower, that is, at the level of the 7th cervical vertebra in most cases. Reports on the Japanese (Nishi, 1921) and on Europeans (Vir- chow, 1914-a) mention the lower limit to be mostly at the level of the spinous process of the 6th cervical vertebra as in the present study. Nishi (1921) mentions that the lower limit of this muscle in the Japanese was at the level of the 1st and 2nd thoracic vertebrae at a considerably high frequency, but in no case in the present study was the lower limit below the 2nd thoracic vertebra. Furthermore, Lanz (1922) reported that in 1 negro who had origin of this muscle from the spinous processes ranging from the 2nd thoracic to lower cervical vertebrae, there was found an additional thin digitation of origin from the spinous process of the 8th thoracic vertebra. However, it is felt that such a finding of the negro is an abnormality (Table 4).

Table 4. Lower limit of the location of the M. interspinalis cervicalis longus (the so-called M. spinalis cervicis).

(b) Mm. interspinales cervicales (breves) These muscles are thin fasciculi which maintain their main plane in sagittal direction, and connect adjacent spinous processes ranging from the axis to the 1st thoracic vertebra. This study revealed the presence of these muscles in all of the interspinous spaces in the area between the axis to the 7th cervical vertebra, but the last muscle, i. e. the muscle connecting the spinous Statistical Observations on the Musculi Interspinales of the Japanese 237 process of the 7th cervical vertebra with that of the 1st thoracic vertebra, was absent in rare cases (3 sides, 5%). There is no mention of the absence of these muscles in the reports of Eisler (1912), Kurz (1922) or Nishi (1939). On the other hand, there is a report (on the Ainu ; Shindo, 1930) which mentions the absence of the last muscle at a considerably high frequency (2 sides out of 10 sides examined, 20%). However, none of these reports, except that of Nishi, were based upon the examination of a large number of cases so that it is dangerous to make a hasty conclusion, but if a bold as- sumption were to be made, it seems that the last muscle may be absent in rare cases (Table 5).

Table 5. Frequency of the Mm. interspinales of the cervical and upper thoracic regions within the respective interspinous spaces.

2. Mm. interspinales thoracales These muscles, as mentioned earlier, were frequently found in the upper thoracic region and always present in the lower thoracic region, but absent in the mid-thoracic region. These muscles will, therefore, be described separately by those in the upper thoracic region and those in the lower thoracic region.

(a) Mm. interspinales of the upper thoracic region These muscles, present in successive continuation with the last M. interspinalis cervicalis, which connects the spinous processes of the 7th 238 Ryosuke Miyauchi

cervical and 1st thoracic vertebrae, are located within the interspinous spaces below the level of the 1st thoracic vertebra, and in no case was there interruption in the presence of this muscle within any of the interlying interspinous spaces. That is, when the last M. interspinalis cervicalis was absent, as noted in rare cases in the present examination (3 sides, 5%), the Mm. interspinales of the upper thoracic region were missing. The general shape of these muscles is similar to that of the last M. interspinalis cervicalis. The location of these muscles within the interspinous spaces was in the range of the 1st to 3rd thoracic vertebra, and they were absent beyond the level of the 3rd thoracic vertebra. Further, the muscle within the interspinous space between the 1st and 2nd thoracic vertebrae was present in many cases (26 sides, 43.3%) and that within the interspinous space between the 2nd and 3rd thoracic vertebrae was found only rarely (3 sides, 5%), but in each of these cases the muscle connecting the spinous process of the 2nd thoracic vertebra with that of the 3rd thoracic vertebra was in successive continuation with the first M. interspinalis thoracalis, which connects the spinous process of the 1st thoracic vertebra with that of the 2nd thoracic vertebra. According to the report of Eisler (1912), the first M. interspinalis thoracalis is occasionally missing and the muscle connecting the spinous process of the 2nd thoracic vertebra with that of the 3rd thoracic vertebra is present only rarely. The findings in his report are similar to the present study. In the Ainu (Shindo, 1930) the frequency of the first M. interspinalis thoracalis (4 sides out of 10 sides, 40%) is similar to that in the present study, but the M. interspinalis of the upper thoracic region was absent in the Ainu beyond the 2nd thoracic vertebra. Furthermore, no report mentions the presence of these muscles beyond the level of the 3rd thoracic vertebra. This is the same as the results of the present study. Therefore, it is assumed that the Mm. interspinales of the upper thoracic region in man, being poorly dif- ferentiated and poorly developed, are not present beyond the 3rd thoracic vertebra although found frequently between the spinous processes of the 1st and 2nd thoracic vertebrae (Table 5).

(b) Mm. interspinales of the lower thoracic region These muscles were always present and moreover were successively continuous with the first M. interspinalis lumbalis below. In no case was this muscle missing in any of the interlying interspinous spaces. These muscles were formed by the combination of flat, board-like muscle bundles which maintained their main plane in sagittal direction and fusiform fasciculi located on their dorsal side. The attachment of these muscles to the spinous process covered the area extending from Statistical Observations on the Musculi Interspinales of the Japanese 239 the tip to the base of the spinous process. This study frequently showed the presence of these muscles in the area below the 10th thoracic vertebra (22 sides, 36.7%), but they usually were found below the 11th thoracic vertebra (95%). In the Ainu it was reported that these muscles were frequently present in the area beyond the 7th thoracic vertebra, although more usually below the 9th thoracic vertebra, and that they were found in the area beyond the 10th thoracic vertebra in all cases (Shindo, 1930). On the other hand, the report of Eisler (1912) mentions that these muscles are located in the area beyond the 11th thoracic vertebra and that it is not infrequent for the muscle in the interspinous space between the 11th and 12th thoracic vertebrae to be missing. The findings of the present examination, therefore, are similar to the report of Eisler, and it can be said that the upper limit of the location of these muscles in the Ainu is considerably more cranial in comparison with the results of this study and the report of Eisler. It seems that the cranialward shift of the upper limit of the location of these muscles in the Ainu may suggest the presence of racial differences (Table 6 and 7).

Table 6. Upper limit of the location of the Mm. interspinales of the lower thoracic region.

3. Mm. interspinales lumbales These muscles were in successive continuation with the last M. interspinalis of the lower thoracic region that connected the spinous processes of the 12th thoracic and 1st lumbar vertebrae and located within the interspinous spaces in the area between the 1st lumbar vertebra to the 1st sacral vertebra. There was no case with absence of this muscle in any of the interlying interspinous spaces. 240 Ryosuke Miyauchi

An exception to this, however, is the muscle within the interspinous space between the 4th and 5th lumbar vertebrae which was missing in rare instances (4 sides, 6.7%). Furthermore, the last one, i. e. the muscle connecting the spinous process of the 5th lumbar vertebra with that of the 1st sacral vertebra, was absent at a considerable frequency (20 sides, 33.3%). The general shape of these muscles was similar to the Mm. interspinales of the lower thoracic region. In the Ainu (Shindo, 1930) the last M. interspinalis lumbalis was present in all cases, whereas it was absent in Chinese newborn (Kurz, 1922). The report of Eisler (1912) mentions that the absence of the last M. interspinalis lumbalis is not infrequent. The findings in the present study are similar to those of Eisler. Although a comparison can not be made due to the lack of reports dealing with large numbers of cases, there does not seem to be any report which mentions the

Table 7. Frequency of the Mm. interspinales of the lower thoracic, lumbar and sacral regions within the respective interspinous spaces Statistical Observations on the Musculi Interspinales of the Japanese 241 absence of the muscle within the interspinous space between the 4th and 5th lumbar vertebrae (Table 7).

4. M. interspinalis sacralis This muscle was found on only 8 sides (13.3%) out of 60 sides examined in this study. In each of these cases, this muscle was in successive continuation with the last M. interspinalis lumbalis and present only between the 1st and 2nd sacral vertebrae. The general shape of this muscle did not differ greatly from that of the Mm. interspinales in the lumbar region. This muscle was reported to be present on 6 sides out of 8 sides examined (75%) in the Ainu (Shindo, 1930). Eisler (1912) also has reported the frequent presence of this muscle. In comparison, the frequency of this muscle was considerably lower in the present study (Table 7).

Summary The purpose of this study was the determination of the normal condition of the Mm. interspinales of the Japanese by the examination of a comparatively large number of cases (30 bodies, 60 sides), and the results of the examinations were processed statistically. The Mm. interspinales of man consist of the Mm. interspinales cervicales, the Mm. interspinales thoracales, the Mm. interspinales lumbales and the M. interspinalis sacralis.

1. Mm. interspinales cervicales These muscles can be subdivided into the M. interspinalis cervicalis longus (the so-called M. spinalis cervicis) which connects the spinous process of one cervical vertebra with that of another cervical vertebra with at least one spinous process interposed between the origin and the insertion, and the Mm. interspinales cervicales (breves) which connect adjacent spinous processes.

(a) M. interspinalis cervicalis longus (the so-called M. spinalis cervicis) This muscle was present at a considerably high frequency (81.7%). The frequency at which it was missing showed no difference by side. The upper limit of the location of this muscle ranged from the 2nd to 4th cervical vertebra, and was most frequently at the level of the 2nd cervical vertebra (73.5%). On the other hand, the lower limit ranged from the 4th cervical to 1st thoracic vertebra, but was most frequently at the level of the spinous process of the 6th cervical vertebra (36.7%). 242 Ryosuke Miyauchi

(b) Mm. interspinales cervicales (breves) These muscles were present in all cases within the interspinous spaces in the area between the 2nd to 7th cervical vertebra, but the last one, I. e. the muscle connecting the spinous process of the 7th cervical vertebra with that of the 1st thoracic vertebra, was missing in rare cases (5%).

2. Mm. interspinales thoracales These muscles were present in the upper and lower thoracic regions, and absent in the mid-thoracic region. These muscles will, therefore, be described separately by those in the upper thoracic region and those in the lower thoracic region.

(a) Mm. interspinales of the upper thoracic region These muscles were present in successive continuation with the last M. interspinalis cervicalis. The location of these muscles was in the range of the 1st to 3rd thoracic vertebra. Moreover, they were frequently present in the interspinous space between the 1st and 2nd thoracic vertebrae (43.3%), but only rarely in the interspinous space between the 2nd and 3rd thoracic vertebrae (5%).

(b) Mm. interspinales of the lower thoracic region These muscles were present in successive continuation, and the last muscle which connected the spinous processes of the 12th thoracic and 1st lumbar vertebrae was continuous with the first M. interspinalis lumbalis below. Although the location of these muscles was in the area beyond the 10th thoracic vertebra in some instances (36.7%), they were more usually present below the 11th thoracic vertebra (95%) and always found beyond the 12th thoracic vertebra.

3. Mm. interspinales lumbales These muscles were located in successive continuation with the last M. interspinalis of the lower thoracic region that connected the spinous process of the 12th thoracic vertebra with that of the 1st lumbar vertebra, and the one within the interspinous space between the 4th and 5th lumbar vertebrae was missing in rare instances (6.7%), while the last one, i. e. the muscle connecting the spinous process of the 5th lumbar vertebra with that of the 1st sacral vertebra, was absent at a considerably high frequency (33.3%).

4. M. interspinalis sacralis This muscle, which is continuous with the last M. interspinalis lumbalis, was found only rarely in the present study (13.3%). Statistical Observations on the Musculi Interspinales of the Japanese 243

References 1) Eisler, P. : Die Muskeln des Stammes. Gustav Fischer, Jena, 1912. 2) Giacomini, C. : cited from Loth. 3) Kurz, E. : Anatomische Untersuchungen tiber die Muskulatur eines neugeboren Chinesenkindes. Ein Beitrag zur Anatomie der gelben Rasse. Z. Anat. u. Entw., 64: 476-532, 1922. 4) Lanz, T. : Die Haut-u. Skelettmuskulatur des Kamernnegers Samuel Jakob. Zsch. f. Morph. u. Anthrop., 22 : 373-434, 1922. 5) Loth, E. : Beitrage zur Anthropologie der Negerweichteile. Stud. u. Forsch. d. Mensch. VOlkerkunde. 9. Stuttgart, 1912. 6) Miyauchi, R. : On the mm. interspinales in man. Acta Anat. Nippon., 50(5) : 272 (Abstract in Japanese), 1975-a. 7) Miyauchi, R. : On the genuine musculus spinalis cervicis in man. In particular the identification of this muscle from the pattern of nerve supply. Med. Bull. Fukuoka Univ., 2(2) : 139-145, 1975-b. *8) Mori, 0. et al. : Anatomy. Vol. 1. 10. ed. Kanehara-Shuppan-Co., Tokyo-Kyoto (in Japanese), 1971. *9) Nishi , S.: Findings on the musculature of the Japanese. The statistical study of museles of the back. Part 2. Tohoku Med. J., 5: 8-23 (in Japanese), 1921. 10) Nishi, S.: Muskeln des Rumpfes. In Bolk et al. : Handbuch der vergleichenden Anatomie der Wirbeltiere. Bd. 5. Urban & Schwanzenberg, Berlin-Wien, 1938. 11) Nishi, S.: Die Riickenmuskeln von Macacus Rhesus. Ein Beitrag zur Myologie der Primaten unter Beriicksichtigung der menschlichen (Versuch einer statisti- schen Anatomie). Jap. J. med. Sci., 1(7) : 153-171, 1939. *12) Shindo , S.: Study of the physical characteristics of the Ainu. Part 3. The muscles of the back, deep muscles of the neck, spinal cord and vertebral column of the Ainu. Jour. of Hokkaido Med. Sci., 8(4) : 111-215 (in Japanese), 1930. *13) Ura , R.: Practice of human anatomical dissection. 11. ed. Nankodo, Tokyo- Kyoto (in Japanese), 1970. 14) Virchow, H.: Ueber die tiefen Riickenmuskeln des Menschen. Vorschlage zur Abanderung der Bezeichnung und Beschreibung derselben. Verh. Anat. Gesellsch., 21 : 91-111, 1907. 15) Virchow, H.: Der Zustand der Riickenmuskulatur bei Skoliose und Kyphoskoliose. Zeitschr. f. orthopadische Chirurgie, 34: 1-91, 1914-a. 16) Virchow, H.: Ueber die Riickenmuskeln des Schimpanse. Arch. Anat. Physiol., Anat. Abt. : 319-350, 1914-b. 17) Virchow, H.: Ueber die Riickenmuskeln des Erythrocebus patas. Arch. Anat. Physiol., Anat. Abt. : 1-58, 1916.

* English titles were translated from Japanese by the present author.