engleski

Unilateral agenesis of intercostal muscles in a dog

Introduction: Intercostal muscles belong to muscles of the thoracic wall. They are distributed in two layers and occupy the space between the ribs. External intercostal muscles originate proximally on caudal border of the ribs, run caudoventrally and terminate on the cranial border of the next rib. Internal intercostal muscles lie under external intercostal muscles and they originate proximally on the cranial border of the more caudal rib, run cranioventrally and terminate on the caudal border of the rib immediately in front. The aim of the study was to show agenesis of both intercostal muscles in a dog. Methods: The study was carried out on one adult male crossbreed dog during the gross anatomy course at the Department of Anatomy, Histology and Embryology, Faculty of Veterinary Medicine, University of Zagreb. Results: During the study of thoracic wall muscles we have observed the absence of both intercostal muscles in the right 5th intercostal space. Fine dissection of the named space showed two layers of connective tissue, the 5th intercostal artery, vein and nerve. Superficial layer was extremely thin and equivalent to external intercostal muscle, while the profound layer was endothoracic fascia. This agenesis of both intercostal muscles appears only on the right side of the thorax. Conclusion: To our knowledge, this study represents the first record of agenesis of both intercostal muscles. Previously, anatomical variations (additional muscle bundles) in pectoral girdle and neck muscles in dogs were observed in relatively high percentage. Considering that the variation has been perceived as an accidental finding during anatomical dissection, and according to anamnestic data, the dog did not have any changes in respiration and behaviour. Consequently, during anatomical dissection considerable attention should be pointed towards the existence of anatomical variations.

dog; muscle variation; agenesis

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