The Serratus Major is a large Muscle having seven or eight Indentings or Jaggs. It takes its rise in the interior Basis of the Omoplata or Shoulder-Blade, and its Jaggings are inserted in
the five lower true Ribs, as also in the two upper spurious Ribs.
The Serratus Posticus Superior, begins with a large Aponeurosis in the Apophyses of the three lower Vertebræ of the Neck, and of the first of those of the Back; then passing under the Rhomboid, it is join'd obliquely by four Indentings to the four upper Ribs.
The Serratus Posticus Inferior, commences in like manner with a large Aponeurosis in the Apophyses of the three lower Vertebra's of the Back, and of the first of those of the Loins, and is afterwards fasten'd by four Digitations to the four lower Ribs.
The eleven External Intercostal Muscles are situated in the spaces between the twelve Ribs passing obliquely and on the outside from the back part to the fore part. They take their rise below the Upper Rib, and have their Insertion above the lower Rib.
The Triangularis is the first of those that contract the Breast, and possesseth the inward part of the Sternum: Its Original is in its lower part, and its Insertion in the top of the Cartilages of the two upper Ribs.
The Sacrolumbus hath its Source in the hinder part of the Os Sacrum, as also in the Vertebra's of the Loins, and ascending from thence, insinuates it self into the hinder part of the Ribs, to every one of which it imparts two Tendons, one whereof sticks on the outside, and the other on the inside. This Muscle is fleshy within, and fibrous without.
The Eleven Internal Intercostals, contrary to the External, derive their Original from the
top of every lower Rib, and ascend obliquely from the back-part to the fore-part, till they are join'd to the lower Lip of every upper Rib: Thus these Internal Muscles, with the External, form, by the opposition of their Fibres, a Figure resembling a Burgundian Cross.
The Diaphragm or Midriff is esteem'd as the fifty seventh Muscle of the Breast, and serves as well for its dilatation as contraction. It separates the Thorax or Chest from the lower Belly, and is tied circularly to all the Extremities of the Bastard Ribs, immediately under the Xiphoides, or Sword-like Cartilage.