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Journal of the Anatomical Society of India

Bilateral presence of muscle 'Stylochondrohyoideus' - A Rare Anomaly

Author(s): Joshi, S. D., Waghmode, P. S. and Joshi, S. S.

Vol. 56, No. 1 (2007-01 - 2007-06)

Joshi, S. D., Waghmode, P. S. and Joshi, S. S.

Rural Medical College, Pravara Rural, University, Loni-413736 Distt. Ahmednagar (Maharashtra)

ABSTRACT:

Inspite of the fact that the blue print of the whole body is unravelled, mysteriously enough, flawlessly and accurately, during the growth and development of an animal; but for some unforseen reasons variations do occur. During routine dissection in a 60 year old male cadaver we found the presence of an anomalous muscle completely replacing the stylohyoid ligament, bilaterally. The muscle was well developed fleshy throughout the whole length except near its insertion on the lesser cornu of hyoid. No attachment of middle constrictor was seen from this muscle. Schafer et al. (1923) have described such a muscle which may accompany or replace the stylohoid ligament and have named it as muscle ‘stylochondrohyoideus’.

KEY WORDS: Stylohyoid, stylochondrohyoideus, styloid process, hyoid arch.

INTRODUCTION

Finding the variations in the muscles of the body is not uncommon. This may or may not have a clinical relevance. They may be traced as a phylogenetic variation which may have been a normal feature down the evolutionary course or may be due to genetic or environmental factors.

Stylohyoid ligament represents the epihyal part of the skeleton of hyoid arch and reviewing the literature one finds that the ligament may be absent, may be very thick, may be cartilaginous or bony, or may show some muscle fibres; but the complete replacement of the ligament by very well developed muscle belly has not been described except by Schafer et al. (1923) who have named it as muscle ‘stylochondrohyoideus’. During routine dissection we came across such a rare anomaly where this muscle was very well developed and present bilaterally. main means of establishing the diagnosis. Genetic counseling cannot be done due to the lack of facilities

Family history- The parent of these two brothers (Case-I, Case-II) had early marriage. At the age of 17 years the mother gave birth to a girl (IUD) by breech presentation. Subsequently she gave birth to five sons and one daughter. The eldest son is suffering at present with cardiac problem. The second (Case-I) and fifth (Case-II) sons having postaxial polydactyly of both hands and feet.

Material and Method

In a sixty year old male cadaver during routine dissection incidently this anomalous muscle (Stylochonodryhyoideus) was found which was bilaterally present. It was thoroughly dissected. displayed and photographed. This resulted in our quest to search for the variations in the muscles of styloid apparatus. We dissected on both sides in 25 cadavers (total 50 specimens) and this muscle was not found in any other specimen dissected.

Observations

This muscle ‘stylochondrohyoideus’ was found bilaterally arising from the tip of styloid process extending downwards and forwards passing deep to the posterior edge of hyoglossus and reaching for its insertion on lesser cornu of hyoid bone as shown in figure. Stylohyoid ligament was absent bilaterally being replaced by this muscle. A fine twig arising from facial nerve could be traced to reach the upper part of this muscle. The fleshy belly of the muscle was well developed and measured 5.5 cms in length on both sides. Fibres of the middle consrictor of the pharynx, which normally arise from lower part of stylohyoid ligament and the lesser cornu of the hyoid were wanting and the middle constrictor arose from only the greater cornu of hyoid to spread out in the wall of pharynx. Other muscle arising from the styloid process, viz. styloglossus, stylopharyngeus and stylohyoid were found to be normal bilaterally.

stylochondrohyoideus

Discussion

Stylohyoid ligament superiorly is attached to the tip of styloid process and running downwards and forwards get attached to lesser cornu of the hyoid bone. The lower part of its posterior margin gives attachment to the fibres of middle constrictor of pharynx. The stylohyoid ligament represents unossified part of the skeleton of the second pharyngeal arch. Keith (1948) has described that this epihyal part of the hyoid arch becomes ligamentous and forms stylohyoid ligaments. Hamilton and Mossmann (1978) and Last described it to arise from perichondrium of the second arch.

Occasionally, the entire ligament is replaced by bone. Williams et al (1995) have described that the ligament may be partially ossified and that in many mammals it forms a distinct bone-epihyal. Buchanan (1950) has stated that epihyal is well seen in intermediate segment of hyoid arch in ruminants.

Variations in the ossification in the intermediate segment leads to much variation in the appearance of styloid process. Hollinshead (1982) quoting Chi-Min described bilateral replacement of this ligament by an anomalous muscle. Schafer et al (1923) have described a distinct muscle ‘stylochondrohyoideus’ passing from the styloid process to the lesser cornu of hyoid, accompanying or replacing stylohyoid ligament. The attachment to the lesser cornu is the commonest termination but it may have other insertions.

Romanes (2000) has described that the stylohyoid ligament may be stout or slender and it is not uncommon to find to partly cartilaginous or ossified, occasionally it may contain muscle fibres.

Bergman et al (1995) have described the variations in stylohyoid muscle. One such variation is a muscle stylohyoideus profundus (stylochondrohyoideus, stylohyoideus novus) which sometimes inserts into lesser cornu of hyoid and may replace stylohyoid ligament but these slips accompany the stylohyoid muscle proper, whereas in the present case its an independent muscle from the tip of the styloid process to the lesser cornu of hyoid replacing the stylohyoid ligament.

Thus the present case report describes a rare anomalous muscle “STYLOCHONDROHYOIDEUS” which is not a variant of stylohyoid muscle.

References:

  1. Bergman R. A. Afifi A K, Miyauchi R; Illustrated Encyclopedia of Human Anatomic Variation in Muscular System. 1996, 38.
  2. F. Wood Jones; Buchanan’s Manual of Anatomy. 8th Edn; Bailliere, Tindall and Cox, London, 1950 pp 1149.
  3. Hamilton W J, Mossaman H W; The Hamilton, Boyd and Mossaman’s Human Embryology: Prenatal Development of Form and Fnction. The Williams and Wilkin’s company, 1978, pp 539-540.
  4. Hollinshead, W.H; Anatomy for Surgeons: The Head and Neck in jaws, palate and tounge. 3rd Edn; Vol I. Harper and Row Publishers. Philadelphia, 1982, pp 364.
  5. Keith Sir A; Human Embryology and Morphology in Pharynx and Neck. 6th Edn; Arnold, London, 1948, pp. 351.
  6. Last R J; Anatomy Regional and Applied. 7th Edn; ELBS Churchill Livingstone, 1984, pp 398, 416.
  7. Romanes G J; Cunningham’s manual of practical anatomy in Head Neck and Brain. 15th Edn; Vol III. Oxford University Press, Oxford, New York, Tokyo. 2000, pp. 135.
  8. Schafer E S, Syrrington J, Bryce T H; Quain’s Elements of Anatomy in Myology. 11th Edn; Vol III. Oxford University Press, Oxfor, New Yord, Tokyo. 2000, pp. 135.
  9. Williams P L, Bannister L H, Berry M M, Collins P, Dyson M, Dussek J E, Ferguson MWJ; Greys anatomy. 38th Edn; Churchill Livingstone, New York, Edinburgh, London, Tokyo, Madrid and Melbourne, 1995, pp. 806.
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