ORIGINAL ARTICLE Variations in Pectoral Girdle Muscles in Dogs I. Alic ´ 1 *, T. Trbojevic ´ Vukic ˇevic ´ 1 , M.  Duras 1 , S. Kuz ˇir 1 , G. Fazarinc 2 and V. Gjurc ˇevic ´ Kantura 1 Addresses of authors: 1 Department of Anatomy, Histology and Embryology, Faculty of Veterinary Medicine, University of Zagreb, Heinzelova 55, 10 000 Zagreb, Croatia; 2 Institute for Anatomy, Histology and Embryology, Veterinary Faculty Slovenia, University of Ljubljana, Gerbic ˇ eva 60, 1000 Ljubljana, Slovenia *Correspondence: Tel.: 00 385 1 2390 259; fax: 00 385 1 2441 390; e-mail: ialic@vef.hr With 3 figures and 2 tables Received July 2012; accepted for publication January 2013 doi: 10.1111/ahe.12042 Summary Muscle variations take the form of additional muscle bundle or belly, unusual muscle origin or termination, as well as complete muscle absence. Knowledge of such variations not only has clinical importance for guiding surgery, but also can help reveal phylogenetic relationships. To improve our understanding of muscle variations in dogs, 57 medium-sized, cross-breed male and female adult animals were dissected as part of a gross anatomy course between 2005 and 2011. Variations in pectoral girdle muscles were observed in 7 (12.3%) dogs and took the form of an additional muscle bundle in the brachiocephali- cus muscle (n = 2), in the omotransversarius muscle (n = 2), in the cervical part of the rhomboideus muscle (n = 2) and in the cervical part of the serratus ventralis muscle (n = 1). Muscle variation was bilateral in only one dog; it involved the omotransversarius muscle. The variations did not seem to be sex dependent. Such variations can appear regularly in dogs and should be taken into consideration during anatomical dissection. Introduction Humans and animals exhibit muscle variations, defined as the appearance of additional muscle bundle or belly, unusual muscle origin or termination, as well as complete absence of a muscle. These variations are usually described in case reports involving humans and less frequently in reports describing domestic animals. Knowledge of muscle variations is clinically significant in human and veterinary medicine because it influences invasive and non-invasive therapeutic procedures. In addition, muscle variations in animals can give insights into phylogenetic relationships. Understanding muscle variations in dogs is particularly important because these animals are the most frequent patients in small veterinary practices, which are perform- ing increasingly complex surgical procedures. Few studies have examined neck and hyoid apparatus muscle varia- tions in these animals (Evans, 1959; Terrado and Ortega, 2002; Terrado et al., 2005; Giner et al., 2009; Gjurc ˇevic ´ Kantura et al., 2010). To our knowledge, no published study has examined variations in the pectoral girdle muscles in dogs. These muscles are important in animal development and may reveal key insights into dog evolu- tion. In addition, understanding their variations may have practical applications in surgical procedures such as treat- ing bite injuries of the shoulder and thoracic wall muscles, thoracotomy and limb amputation. The muscles of the pectoral girdle originate on the neck, back and chest and extend to the shoulder or brachium, reaching as far as the elbow joint (Miller et al., 1964). In domestic animals, they join the forelimb to the trunk, forming a connection known as a synsarcosis that substitutes for a conventional joint (Dyce et al., 2010). A superficial layer of the pectoral girdle muscles lies directly upon the fascia of the shoulder and brachium and includes the trapezius, omotransversarius, brachiocephali- cus, pectoralis superficialis and latissimus dorsi muscle. The deeper layer represents the rhomboideus, serratus ventralis and pectoralis profundus muscle. Table 1 pro- vides a brief description of the pectoral girdle muscles in dogs (Miller et al., 1964; Nickel et al., 1986; K€ onig and Liebich, 2006; Schaller, 2007; Dyce et al., 2010; Evans and de Lahunta, 2010). © 2013 Blackwell Verlag GmbH Anat. Histol. Embryol. 43 (2014) 16–21 16 Anatomia, Histologia, Embryologia