engleski

Anatomical variation of the scalenus dorsalis muscle in a dog

Introduction: Scalenus muscles in the dog are represented by scalenus medius and scalenus dorsalis. Scalenus medius muscle arises with three, more and less separated bundles on the cranial border of the first rib. The two deeper bundles are inserted on the transversal processes of the 7th and 6th cervical vertebrae. The ventral superficial bundle runs from the first rib cranialy to the transversal processes of the 5th, 4th and 3rd cervical vertebrae. Scalenus dorsalis muscle consists of two or three separate muscle bundles. The dorsal bundle arises on the 3rd rib, the middle bundle on the 4th rib or together with the dorsal bundle. The ventral bundle is the longest and it arises from the 8th or 9th rib. The dorsal bundle terminates on the transversal processes of the 5th, 4th and sometimes the 3rd cervical vertebrae. Methods: The study was performed on a crossbred dog during the gross anatomy course at the Department of Anatomy, Histology and Embryology, Faculty of Veterinary Medicine, University of Zagreb. Results: The established muscle variation was observed unilaterally, on the left side of the thorax. During anatomical dissection we have observed small and thin additional muscle bundle which separates from the ventral border of the scalenus dorsalis muscle. This additional muscle bundle originated from the ventral third of the 4th rib and was located dorsally to the rectus thoracis muscle. Conclusion: To our knowledge, this research represents the first record of additional muscle bundle in scalenus dorsalis muscle in a dog. Findings of additional muscle bundles are primarily important for anatomists and embryologists, but are becoming more important in surgical procedures applied in certain body regions. We consider that the variations were a consequence of parallel evolution of the locomotor and nervous system, as well as possible backwardness of myotome during their migration.

dog; muscle variation; additional muscle bundle

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