The _Pronator Superior Rotundus_, or round Muscle of the _Radius_, commenceth from the inner _Apophysis_ of the Shoulder-Bone, in a very fleshy Stock, and is terminated obliquely by a Membranous _Tendon_ in the middle and exterior part of the _Radius_. The _Pronator Inferior Quadratus_, springing forth from the bottom and inside of the _Cubitus_, is fixt in the lower and outward part of the _Radius_ by a Tail as large as its Head. This Muscle lying hid under the others near the Wrist, is that which jointly with the _Rotundus_, turns the Arm with the Palm of the Hand downward, which is the Motion of _Pronation_. The _Longus_ is the first of the _Supinators_, whose Origine is three or four Fingers breadth above the external _Apophysis_ of the Arm-Bone; from whence it passeth along the _Radius_, and cleaves to the inner-part of its lower _Apophysis_. {43} The _Brevis_, or the second of the _Spinators_ arising from the lower part of the _Inferior Condylus_, and the external of the _Humerus_, is twisted round about the _Radius_, going forward from the hinder-part till it is united to its upper and forepart. This Muscle, with the _Longus_, serves to turn the Arm and the Palm of the Hand upward, and produceth the Motion of _Supination_. _How many sorts of Motions belong to the Wrist, and what are its Muscles_? Two several Motions are perform'd by the Wrist, _viz._ one of Flection, and the other of Extension, three Muscles being appropriated to the former, and as many to the later: But it ought to be observed, that a strong Ligament, call'd the _Annular_, appears here, which, surrounding all the _Tendons_ of the Muscles as it were a Bracelet, holds them together, and elsewhere serves to unite the two Bones of the Elbow. The three Flexors or Bending Muscles of the Wrist are the _Cubitæus Internus_, the _Radiæus Internus_, and the _Palmaris_. The _Cubitæus Internus_ derives its Original from the part of the Arm-Bone, passeth under the Annular Ligament, and is ty'd by a thick _Tendon_ to the small Bone of the Wrist, which is plac'd above the others. The _Radiæus Internus_ proceeds from the same place with the _Cubitæus_, and is fasten'd to the first Wrist-Bone which supports the Thumb. It lies along the _Radius_, and passeth under the _Annular_ Ligament. The _Palmaris_ is reckon'd among the Flexors of the Wrist, although situated in the Palm of the Hand. It ariseth from the inner Process or Knob {44} of the Arm-Bone, and is united by a large _Tendon_ to the first _Phalanges_ of the Fingers, slipping under the Transverse or _Annular_ Ligament and sticking under the Skin of the Palm of the Hand. The three extending Muscles of the Wrist are the _Cubitæus Externus_, and the _Radiæus Externus_ or the _Longus_, and the _Brevis_. The _Cubitæus Externus_ taking its rise from the hinder-part of the Elbow, passeth under the _Annular_ Ligament, and adheres to the upper and outward-part of the Bone of the _Metacarpus_ that stayeth the little Finger.