The Function and Service of Muscles.

See the arranged Trapezius, shown at figure C.

Function and Placement of the Visible Muscles of the Arm and those serving its movement.

14.

Deltoides, or Triangular Shoulder Muscle, is the muscle that lifts the arm in various ways. It begins in the middle of the collarbones (14) and the spine of the shoulder blade (17) and ends with a strong tendon in the middle of the humerus (22). Its companion is the Supra-Spinatus or Upper Ridge Muscle. It spreads from the hollow area above the back or the spine of the shoulder blade and inwardly in the hollow shoulder bone (22). It is not outwardly visible. See the Deltoides muscle in the illustration B. C.

15.

Infra-Spinatus or Lower Ridge Muscle. This muscle pulls down alongside the Rotundus Major (16) and Latissimus (17), moving the arm backward in various ways. It spreads closely under the spine of the shoulder blade (17), broadly spread and fleshy; filling the entire hollow that is under the mentioned spine, and it connects in the neck and head of the humerus (22) (23) with a Thick and Broad Cord. See the illustration B. C.

16.

Rotundus Major. This muscle pulls down similarly to the aforementioned Infra-spinatus (15) and the following Latissimus (17). It moves the arm backward, in diverse ways: it spreads from the lower ribs of the shoulder blade (19) and connects in the ...

Translation Notes

Supra-Spinatus: could also be referred to as the "Upper Spine Muscle".
Deltoides: refers to what is commonly known today as the Deltoid muscle.
Rotundus Major, also known as the Teres Major muscle, which assists in arm movement.
Latissimus: refers to the Latissimus Dorsi, a large muscle of the back.