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Polypterus and the evolution of fish pectoral Musculature

Published at:ÌýJournal of Anatomy, (2015) 226, pp511—522

Authors:ÌýBenjamin C. Wilhelm, Trina Y. Du, Emily M. Standen and Hans C. E. Larsson, Redpath Museum, ³ÉÈËVRÊÓƵ, Montreal, QC, Canada

Method:Ìý

Pectoral anatomy of polypterus senegalus reconstructed from microCT scan data

Fig. 1 Phylogeny of fishes. Some silhouettes are from and others are original. Figures are not to scale.

Fig. 2 Pectoral anatomy of Polypterus senegalus (A) Polypterus in left lateral view, showing the resting position of the lobed-pectoral fin. (B) Left fin and partial girdle in lateral and (C) medial views. ab.pro., abductor profundus; ab.sup., abductor superficialis; ad, adductor; cmt.I, coracometapterygialis I; cmt.II, coracometapterygialis II; zp, zonopropterygialis. Scale bars: 2 cm.

Fig.3 Pectoral anatomy of Polypterus senegalus reconstructed from microCT scan data. (A) Left fin and girdle in lateral view, with (B) abductor superficialis and (C) abductor profundus removed. (D) Left fin and girdle in medial view, with (E) adductor and (F) zonopropterygialis removed. (G) Posterior view. (H) Cross-section through the proximal fin.

Note: ab.pro., abductor profundus; ab.sup., abductor superficialis; ad, adductor; cl, cleithrum; cmt.I, coracometapterygialis I; cmt.II, coracometapterygialis II; sc, scapulocoracoid; scl, supracleithrum; zp.m., zonopropterygialis medialis. Scale bars: (A–F) 5 mm, (E) 1 mm.

Results:

Using gross anatomical dissection (Fig. 2) and microCT scanning (Fig. 3; Supporting Information Fig. S1), we were able to recognize six independent muscles originating on the pectoral girdle and crossing the glenoid to insert onto the basal endoskeleton of the fin (Table 2). These muscles were distinct from their origin to insertion in the microCT scans, support for their being independent muscles rather than sub-divisions of the abductor and adductor. In cases where two origins were distinct but the muscles could not be separated at their insertion, the two were considered sub-divisions of the same muscle (e.g. the ventral and lateral heads of the abductor profundus and adductor). Overall, this new description varies in a few details but does not conflict greatly with most previous descriptions, with the exception of whether certain muscles are considered independent of the abductor and adductor.

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