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Show 776 MR. ST. GEORGE MIVART ON THE [June 27, latter by the summit of the brachialis anticus and by the insertion of the epicoraco-humeral. Externally the pectoralis major is intimately connected with the outermost layers of the external oblique, while posteriorly, as Meckel remarks*, it is similarly united with the rectus abdominis, of which, indeed, it has every appearance of being the anterior continuation. Costo-coracoid (figs. 7 & 9, C. Ci). A thin sheet of muscular fibres arises from the anterior margin of the first sternal rib, and is inserted into the deep surface of that strong tendon which is described below as in part the origin of the internal long head of the triceps. This tendon passes from the posterior end of the inner surface of the sternum (close to the hinder end of the edge by which it articulates with the coracoid), upwards to the anterior border of the scapula, between the spinous process projecting from that border and the point of attachment of the clavicle, and dividing the anterior (or lower) part of the subscapularis from its posterior portion. This muscle answers no doubt to that which, in the Echidna^, goes from the first rib to the coracoid ; for I have found such a muscle in Alligator lucius, and it is noticed by the Rev. Dr. Haughton in the Crocodile*}; under the name "pectoralis secundus"-a term I would readily adopt, but that I am inclined to think that the muscle may be the homologue of either the pectoralis minor or the subclavius. Stannius § speaks of it as the sterno-scapular; but this name has been applied to a muscle widely different ||. Serratus magnus and levator anguli scajmlce (figs. 2 & 7, S. Mg.). Several small sheets of muscle proceed- from certain ribs to the posterior margin and inner surface (towards^ the superior margin) of the scapula. These may perhaps include, besides the true serratus magnus, not only the levator anguli scapulce, but also the rhomboideus, though I am inclined to regard the latter muscle as absent iu the Iguana, not having succeeded in finding the muscle which Meckel speaks of *f[ as having the same disposition in that animal as in the Chameleon, though absent in Polychrus marmoratus. There appear to be four principal portions of this complex muscle: - (1) The largest and most posterior portion arises from the outer surfaces of the last two cervical ribs (i. e. those of the eighth and ninth cervical vertebrae) near their free ends. Each rib gives rise to a distinct muscular layer; and these layers are inserted, in common, into about the upper half of the posterior (or axillary) border of the scapula (fig. 1, S.Mg. 1). At the lower end of its insertion it is sliglitly embraced by fibres of the subscapularis, a few of which arise externally to it. * Loc. cit. p. 343. t Trans. Linn. Soc. 1866, vol. xxv. p. 382. J Scientific papers read before the Royal Irish Academy, and published in its ' Proceedings,' 1866, vol. i. p. 702. § Loc. cit. p. 122. || Proc. Zool. Soc. 1865, p. 338, and 1866, p. 3*J8 and figs. 2 & 3, S. s. •ft Loc. cit. p. 312. |