Fig. 8

Putative evolutionary origin of the diaphragm through a partial duplication of MMP population. Based on Hirasawa and Kuratani [110]. Left lateral views. a Subcoracoscapular muscle (subscapular muscle-homolog) of the dorsomedial forelimb muscle group and the supracoracoid muscle of the ventrolateral forelimb muscle group in a Pelycosaur-grade taxon, Dimetrodon (based on Romer [19]). b Subscapular muscle and the diaphragm, which evolved from the subcoracoscapular muscle of Pelycosaur-grade ancestors, in an extant mammal, Didelphys (based on Jenkins and Wejs [304]). c Supraspinatus and infraspinatus muscles in Didelphys. Note the cranial margin of the scapula (*) in (a) corresponds to the border between the supraspinatus and infraspinatus fossae (*) in (c) [117, 305]. acr, acrominon; dph, diaphragm; isf, infraspinatus fossa; isp, infraspinatus muscle; hum, humerus; mtc, metacoracoid; prc, procoracoid; sbcs, subcoracoscapular muscle; sbs, subscapular muscle; scap, scapula; spc, supracoracoid muscle; ssf, supraspinatus fossa; ssp, supraspinatus muscle