Absence of scalenus anterior muscle.
A rare anomaly of the scalenus muscles is described. In this case, the right scalenus anterior muscle was absent. As a substitute for this muscle, some aberrant muscle slips arose from the lower vertebrae and descended in front of the ventral rami of the lower cervical nerves. These aberrant slips then ran between the ventral rami of the the eighth cervical and first thoracic nerves, and were fused with the right scalenus medius muscle. Thus, the subclavian artery and vein ran in front of the aberrant slips, together with the ventral ramus of the first thoracic nerve. The aberrant muscle slips issued 2 accessory bundles. One bundle ran between the ventral rami of the fourth and fifth cervical nerves and was fused with the scalenus medius muscle; the other bundle ran between the ventral rami of the fifth and sixth cervical nerves and was fused with the scalenus medius muscle.
Murakami
Shinichiro
S
Department of Human Morphology, Okayama University Graduate School of Medicine and Dentistry, Okayama 700-8558, Japan.
Horiuchi
Kanji
K
Yamamoto
Chugo
C
Ohtsuka
Aiji
A
Murakami
Takuro
T
D000368:Aged; D000369:Aged, 80 and over; D002574:Cervical Vertebrae; D005260:Female; D006801:Humans; D009334:Neck Muscles / Q000002:abnormalities* / Q000294:innervation; D009420:Nervous System / Q000473:pathology; D013348:Subclavian Artery / Q000473:pathology; D013350:Subclavian Vein / Q000473:pathology; D013909:Thorax / Q000294:innervation