Modern Anatomists have discover'd that the Diaphragm is compos'd of two Muscles, viz. one Upper, and the other Lower; so that the Upper cleaves to the Extremities of the Spurious Ribs, and is terminated in a flat Tendon in the middle, which hath been always taken for its Nervous part. The Lower begins with two Productions, the longest whereof being on the right side, ariseth from the three upper Vertebra's of the Loins, and the other on the Left from the two Vertebra's of the Back, till it is lost in the Aponeurosis of the Upper Muscle.
How many Muscles are there in the Back and the Loins, and which be they?
There are three in each side, viz. one for Flection, and the other for Extension.
The Triangularis is the Flexor, taking its rise in the hinder part of the Rib of the Os Ilion, and the inner part of the Os Sacrum, in passing from whence it is joined to the last of the
Bastard Ribs, and to the transverse Productions of the Vertebra's of the Loins.
The Extensors are the Sacer, and the Semi-spinatus, which make the Waste streight, and are so interwoven along the Back-Bone, that one would imagine that there were as many Pairs of Muscles as Vertebra's, affording Tendons to all.
The Sacer springs from behind the Os Sacrum, as also from the hinder and upper Extremity of the Os Ilium, and is inserted in the Spines of the Vertebra's of the Loins and Back.
The Semi-spinatus hath its Source in the Spines of the Os Sacrum, and is join'd to all the transverse Productions of the Vertebra's from the Back to the Neck, being exactly situated between the Sacer and the Sacrolumbus.