Origin and distribution of the brachial plexus in the Spix's yellow-toothed cavy (Galea spixii Wagler, 1831) (Rodentia, Caviidae)

Abstract

Due to the absence of literature on the brachial plexus in the Spix's yellow-toothed cavy, this study was conducted to examine the origin and neural distribution of this rodent's brachial plexus. Ten adult animals obtained from previous experiments were thawed, fixed in 10% formalin solution for 72 h and then dissected. Cotton blocks soaked in 2% hydrogen peroxide were placed on the ventral roots of the plexus. Photographs of the most representative specimens were taken and schematic sketches were prepared to illustrate the results. The Spix's yellow-toothed cavy's brachial plexus primarily originated from the ventral roots of the sixth (C 6 ), seventh (C 7 ) and eighth (C 8 ) cervical nerves and from the first two thoracic nerves (T 1 , T 2 ), and less frequently from C 6 -T 1 or C 6 -T 3 . The peripheral nerve trunks of the Spix's yellow-toothed cavy's brachial plexus are the following: suprascapularis (C 6 -C 7 ), axillaris (C 6 -C 7 ), subscapulares (C 6 -C 7 ), cranial pectoral (C 6 -C 7 ), musculocutaneous (C 7 -C 8 ), radialis (C 7 -T 2 ), medianus (C 7 -T 2 ), ulnaris (C 7 -T 2 ), pectorales caudales (C 7 -C 8 ), thoracicus longus (C 7 -C 8 ), thoracicus lateralis (C 7 -T 2 ) and thoracodorsalis (C 7 -T 2 ).Keywords: anatomy; brachial plexus; nervous system; rodent; Galea spixii List of abbreviations C 6 = ventral root of C 6 ; C 7 = ventral root of C 7 ; C 8 = ventral root of C 8 ; T 1 = ventral root of T 1 ; T 2 = ventral root of T 2 ; T 3 = ventral root of T 3

Anatomy of the brachial plexus in the Mongolian gerbil (Meriones unguiculatus Milne-Edwards, 1867)

“…The suprascapular nerve had as its most frequent origin the branches C 4 and C 5 , and its nervous territory consists of the supraspinal and infraspinal muscles, differing from that described by Guimaraes et al (2013) when studying the plexus in the nutria and by Aydin (2003) in the thorn hog where the roots C 5 and C 6 were described. These results also differ from our previous study in Spix's yellow-toothed cavy (Araujo Jr et al 2016), where we found that it emerges from C 6 and C 7 . The C 6 or C 7 branches do not participate in the formation of this nerve in the gerbil.…”

“…Scavone et al (2008) reported in the spotted paca the origin of this nerve only from C 6 , while Gamba et al (2007) in the chinchilla describe the origin in C 6 and C 7 , differing from what is observed in the gerbil. The cranial pectoral nerve is similar to that found in rats (Greene 1963), emerging from C 5 and C 6 , and it is different in the nutria (Guimaraes et al 2013), which emerges solely from C 6 , in Spix's yellow-toothed cavy (Araujo Jr et al 2016), in which both nerves are formed by C 6 and C 7 and also in the chinchilla (Gamba et al 2007) where it is formed only from C 7 .…”

“…The origin of the gerbil brachial plexus resembles that described by Greene (1963) in rats (Mus nor- Sakai 1997). On the other hand, it differs from that found in the guinea pig (Cooper and Schiller 1975), which consists of the branches C 5 to T 2 ; in the chinchilla (Gamba et al 2007) and the nutria (Guimaraes et al 2013) the brachial plexus consists of C 6 to T 1 , and in Spix's yellow-toothed cavies (Araujo Jr et al 2016) it consists of C 6 to T 2 . None of these formations were found in the gerbil.…”

“…In both cases, the situation is different in the gerbil. As for the axillary nerve, in the red squirrel (Aydin 2011), it stems from C 5 and C 6 ; in the rat (Greene 1963), in the chinchilla (Gamba et al 2007) and in Spix's yellow-toothed cavy (Araujo Jr et al 2016) it consists of C 6 and C 7 , differing from what is observed in the gerbil, since the latter do not have the branches C 5 or C 7 .…”

“…The musculocutaneous and axillary nerves emerge from C 5 to C 7 and they are distributed to the coracobrachial, brachial and biceps brachial muscles, subscapular and deltoid muscles, respectively. In the chinchilla (Gamba et al 2007), the musculocutaneous and axillary nerves have a common origin in C 6 and C 7 , whereas in Spix's yellowtoothed cavy (Araujo Jr et al 2016), these nerves stem from C 7 and C 8 . In both cases, the situation is different in the gerbil.…”