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CHAP. XIX. Of the Muscles of the Shoulder-blade.
NOw we must describe the Muscles of the extreme parts; and first of the Arm, taking our beginning from those of the Shoulder-blade. But first, that we may the better under∣stand their description, we must observe the nature and condition of the Shoulder-blade. Therefore the Blade-bone on that part, which lies next unto the Ribs, is somewhat hollowed;* 1.1 wherefore on the other side it somewhat bunches out. It hath two Ribs, one above, another be∣low; by the upper, is meant nothing else, than a border or right-line, which looking towards the Temples is extended from the exterior angle thereof under the Collar-bone, even to the Pro∣cess Coracoides which this Rib produces in the end thereof: By the lower, the underside which lies towards the Lower-belly and the Short-ribs.
Besides, in this Shoulder-blade we observe the Basis, Head, and Spine.* 1.2 By the basis we under∣stand the broader part of the Shoulder-blade, which looks towards the Back-bone. By the Head we understand the narrower part thereof, in which it receives the head of the Arm in a cavity,* 1.3 in∣ned ferently hollow, which it produces both by it self, as also by certain Gristles, which there fast-encompass that cavity. This kind of cavity is called Glene.
This receives and contains the Bone of the Arm, by a certain strong Ligament encompassing and strengthening the Joynt, which kind of Ligament is common to all other Joynts: this Liga∣ment arises from the bottom of the cavity of the Shoulder-blade, and circularly encompasses the whole joynt, fastning it self to the head of the Arm; there are also other Ligaments beside this, which encompass and strengthen this articulation. By the Spine is meant a process,* 1.4 which rising by little and little upon the gibbous part of the blade, from the basis thereof where it was low and deprest, becomes higher until it ends in the Acromion, or upper part thereof.* 1.5 Nature hath made two productions in this Bone (that is to say, the Acromion from the Spine,* 1.6 and the Coracoides from the upper side) for the strengthening of the articulation of the Arm and Shoulder-blade, that is, lest the Arm should be easily strained upward or forwards; besides, it is fastned to the clavicle, by the process Acromion.
The Muscles which move the Shoulder-blade are six in number, of which four are proper, and two common. The first of the four proper seated in the fore-part, ascends from the bones of five or six of the upper Ribs, to the Coracoides, which it draws forwards, and is called Serratus minor,* 1.7 i. e. the lesser Saw-muscle; which that you may plainly shew, it is fit you pull the pectoral Muscle from the the Collar-bone, almost to the middle of the Sternon. The other first opposite against it is placed on the fore-side, and draws its original from the three lower Spines of the Neck, and the three upper of the Chest, from whence it extends it self, and ends into all the gristly basis of the Shoulder-blade, drawing it backwards; It is called the Rhomboides. The third from its action,* 1.8 is called the Levator, or the Heaver, or lifter up: seated in the upper-part,* 1.9 it descends from the trans∣verse processes of the four first Vertebrae of the Neck into the upper Angle and Spine of the blade. The fourth called Trapezius, or the Table-muscle, is seated in the back-part,* 1.10 and is membranous at the original, but presently becomes fleshy: it arises from almost all the back-part of the head, from all the Spines of the Neck, and the eight upper Vertebrae of the Chest, and then is inserted by his nervous part, almost into the whole basis of the blade, extending it self above the Muscles thereof, even to the midst of the Spine, where being fleshy it is inserted even to the Acromion, the upper part of the Clavicle, and in some sort to the upper-rib. This Muscle hath a threefold action, by reason of its Triple original. The first is to draw the Shoulder-blade towards its original, that is, to the Nowl, and Spine of the Neck; the other is to draw it towards the Back, because of the contraction of the middle or transverse fibers, which lead it directly thither; and the other to draw it downwards by reason of the original it hath from the fifth, sixth, seventh, and eighth Spine of the Vertebrae of the Chest.
But we must note, that these divers actions are not performed by this Muscle, by the assistance of one only Nerve, but by more, which come into it by the Spinal-marrow, by the holes of the Vertebrae, as well of the Neck as the Chest, from whence it takes the original. For the two other which are the common Muscles of the Blade, and Arm, or Shoulder, we will describe them with the Muscles of the Shoulder or Arm: for one of these which is called the Latissimus, that is,* 1.11 the broadest, ascends from the Holy-bone to the Shoulder-blade and Arm.
The other named the Pectoralis comes from the Sternon and Collar-bone,* 1.12 to the Shoulder-blade and Arm.