Departamento de Cirurgia, Faculdade de Medicina Veterina ´ria e Zootecnia, Universidade de Sa ˜o Paulo (USP), Av. Prof. Dr. Orlando Marques de Paiva, 87, Sa ˜o Paulo, Brazil Sex-related Macrostructural Organization of the Deer’s Brachial Plexus S. R.Melo 1 , A. F. N. Gonc¸alves 2 , T. H. de Castro Sasahara 1 , E. T. Fioretto 1 , S. H. Gerbasi 3 , M. R. F. Machado 3 , G. C. Guimara ˜es 3 , A. A. C. M. Ribeiro 1 * Address of authors: 1 Department of Surgery, College of Veterinary Medicine, University of Sa ˜o Paulo (USP), Sa ˜o Paulo, Brazil; 2 College of Animal Science, Sa ˜o Paulo State University (UNESP), Dracena, Brazil; 3 Department of Animal Morphology and Physiology, Sa ˜o Paulo State University (UNESP), Jaboticabal, Brazil; *Corresponding author: Tel.: 05508-000; fax: 55 11 3 7805; e-mail: guto@usp.br With 2 figures and 2 tables Received June 2006; accepted for publication November 2006 Summary We describe the morphological organization of the deer bra- chial plexus in order to supply data to veterinary neuroclinics and anaesthesiology. The deer (Mazama gouazoubira) brachial plexus is composed of four roots: three cervical (C6, C7 and C8) and one thoracic (T1). Within each sex group, no varia- tions are observed between the left and the rightbrachial plexus, though sex-related differences are seen especially in its origin. The origin of axillary and radial nerves was: C6, C7, C8 and T1 in males and C8–T1 (radial nerve) and C7, C8 and T1 (axillary nerve) in females; musculocutaneous nerve was: C6– C7 (males) and C8–T1 (females); median and ulnar nerves was: C8–T1 (males) and T1 (females); long thoracic nerve was: C7 (males) and T1 (females); lateralthoracic nerve was: C6, C7, C8 and T1 (males) and T1 (females); thoracodorsal nerve was: C6, C7, C8 and T1 (males) and C8–T1 (females); supra- scapularnervewas:C6–C7 (males)and C6 (females)and subscapular nerve was: C6–C7 (males) and C7 (females). This study suggests that in male deer the origin of the brachial plexus is more cranial than in females and the origin of the brachial plexus is slightly more complex in males, i.e. there is an additional number of roots (from one to three). This sexual dimorphism may be related to specific biomechanical functions of the thoracic limb and electrophysiological studies may be needed to shed light on this morphological feature. Introduction Deer of six differentgenera, i.e. Blastocerus, Hippocamelus, Ozotoceros, Pudu,Odocoileusand Mazama are endemic to South America. The organization of brachial plexus has been investigated by numerous studies in humans (Baranowski and Pither,1990; Urban and Urquhart,1994)and in animalsbecause ofits direct application in the diagnosis of neuromuscular dysfunc- tions occurring as a result of traumatic processes, infections or neoplasias (Fioretto et al., 2003). This knowledge may also provide anatomical subsidies for local or regionalanaesthesia, thus increasing the analgesic effectduring the transoperative period (Koizumi and Sakai, 1995, 1997;Booth et al., 1997;Nakamura et al., 2004). Regional anaesthesia of the brachial plexus has its advantages and can be used during surgical procedures on the superior limb (Umrey, 1996),presentingnegligiblemorbidityand mortality rates when comparedwith generalanaesthesia (Christopherson et al., 1993; Futema et al., 1999; Estebe et al., 2003).In some species,such aslargeruminants,regional anaesthesia is the only possibility because of the increased risks associatedwith generalanaesthesia (Bhojani et al., 1981). In this study, the macrostructural organization ofthe brachialplexusis investigated in Mazama gouazoubira, a medium-sized wild ruminant weighing 17–23 kg, having greyish or brownish skin and large ears (Duarte and Merino, 1997). Additionally, both males and females are investigated to figure out whether sex differences play a role in the macrostructural organization of the brachial plexus. The knowledgeof the anatomy and physiology of this species may help biologists to preserve them. Hence,in this paper, we describe the morphology of the brachial plexus and the distribution of its nerves in order to supply data to both veterinary and human neuroclinics and anaesthesiology. Materials and Methods Adult deer (M.gouazoubira), seven males and seven females, weighing 15–20 kg were investigated in this study. Animals were obtained already dead and frozen from the Animal’s House of the Biosciences Institute at Sa ˜o Paulo State University (UNESP), Botucatu, Sa ˜o Paulo, Brazil. The specimens were fixed with 10% aqueous formaldehyde solution for 72 h. Following fixation, the brachial plexus was dissected through a ventro-lateral incision of the skin from the thorax to the axillary region. Each root that contributed to the formation of the plexus,nervesand their brancheswere isolated and identified together with muscles and vessels. In order to improve the visualization, the axillary region was immersed in a 60% alcoholic solution of acetic acid and 20% hydrogen peroxidewas applied to clarify the area. The formation of the brachial plexus was carefully dissected using a Leica M651 (Leica Microsystems, Heerbrugg, Germany) experimental surgical microscope (6–40·) and the terminology of the International Committee on Veterinary Gross Anatomical Nomenclature (1994) wasadopted in orderto describe the structures observed. Results The brachialplexus ofM. gouazoubira is composed of four roots:three cervical nerve roots (C6,C7 and C8) and one 2007 The Authors. Journal compilation 2007 Blackwell Verlag www.blackwell-synergy.com Anat. Histol. Embryol. 36, 295–299 (2007) doi: 10.1111/j.1439-0264.2007.00765.x ISSN 0340–2096