Pectoral Girdle

The pectoral girdle (shoulder girdle) supports the arm. It consists of two bones on each side of the body: the clavicle (collarbone) and the scapula (shoulder blade). The medial end of the clavicle articulates with the sternum at the sternoclavicular joint, and its lateral end articulates with the scapula at the acromioclavicular joint (see fig. 8.27). The scapula also articulates with the humerus at the humeroscapular joint. These are loose attachments that result in a shoulder far more flexible than that of most other mammals, but they also make the shoulder joint easy to dislocate.

_Think About It_

How is the unusual flexibility of the human shoulder joint related to the habitat of our primate ancestors?

Clavicle

The clavicle46 (fig. 8.30) is a slightly S-shaped bone, somewhat flattened dorsoventrally and easily seen and palpated on the upper thorax (see fig. B.1b in atlas B). The superior surface is relatively smooth, whereas the inferior surface is marked by grooves and ridges for muscle attachment. The medial sternal end has a rounded, hammerlike head, and the lateral acromial end is markedly flattened. Near the acromial end is a rough tuberosity called the conoid tubercle—a ligament attachment that faces toward the rear and slightly downward. The clavicle braces the shoulder and is thickened in people who do heavy manual labor. Without it, the pectoralis major muscles would pull the shoulders forward and medially, as occurs when a clavicle is fractured. Indeed, the clavicle is the most commonly fractured bone in the body because it is so close to the surface and because people often reach out with their arms to break a fall.

Scapula

The scapula (fig. 8.31) is a triangular plate that dorsally overlies ribs 2 to 7. The three sides of the triangle are called the superior, medial (vertebral), and lateral (axillary) borders, and its three angles are the superior, inferior, and lateral angles. A conspicuous suprascapular notch in the superior border provides passage for a nerve. The broad anterior surface of the scapula, called the subscapular fossa, is slightly concave and relatively featureless. The posterior surface has a transverse ridge called the spine, a deep indentation superior to the spine called the supraspinous fossa, and a broad surface inferior to it called the infraspinous fossa.47 The scapula is held in place by numerous muscles attached to these three fossae.

The most complex region of the scapula is its lateral angle, which has three main features:

1. The acromion48 (ah-CRO-me-on) is a platelike extension of the scapular spine that forms the apex

47supra = above; infra = below

48acr = extremity, point + omi = shoulder

Saladin: Anatomy & I 8. The Skeletal System I Text I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

272 Part Two Support and Movement

Table 8.6 Anatomical Checklist for the Vertebral Column and Thoracic Cage

Vertebral Column

Table 8.6 Anatomical Checklist for the Vertebral Column and Thoracic Cage

Vertebral Column

Spinal Curvatures (fig. 8.19)

Cervical Vertebrae (figs. 8.24 and 8.25a)—(Cont.)

Cervical curvature

Posterior tubercle

Thoracic curvature

Lateral mass

Lumbar curvature

Superior articular facet

Pelvic curvature

Inferior articular facet

General Vertebral Structure (figs. 8.22 and 8.23)

Transverse ligament

Body (centrum)

Axis

Vertebral foramen

Dens (odontoid process)

Vertebral canal

Thoracic Vertebrae ((ig. 8.25b)

Vertebral arch

Superior costal facet

Pedicle

Inferior costal facet

Lamina

Transverse costal facet

Spinous process

Lumbar Vertebrae ((ig. 8.25c)

Transverse process

Sacral Vertebrae (fig. 8.26)

Superior articular process

Sacrum

Inferior articular process

Anterior sacral foramina

Intervertebral foramen

Posterior sacral foramina

Inferior vertebral notch

Median sacral crest

Superior vertebral notch

Lateral sacral crest

Intervertebral Discs (fig. 8.22)

Sacral canal

Annulus fibrosus

Sacral hiatus

Nucleus pulposus

Auricular surface

Cervical Vertebrae (figs. 8.24 and 8.25a)

Superior articular process

Transverse foramina

Alae

Bifid spinous process

Coccygeal Vertebrae ((ig. 8.26)

Atlas

Coccyx

Anterior arch

Cornu

Anterior tubercle

Posterior arch

Thoracic Cage

Sternum (fig. 8.27)

Rib Features (fig. 8.28)

Manubrium

Head

Suprasternal notch

Superior articular facet

Clavicular notch

Inferior articular facet

Sternal angle

Neck

Body (gladiolus)

Tubercle

Xiphoid process

Angle

Rib Types (fig. 8.27)

Shaft

True ribs (ribs 1-7)

Costal groove

False ribs (ribs 8-12)

Costal cartilage

Floating ribs (ribs 11 and 12)

Saladin: Anatomy & I 8. The Skeletal System I Text I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition of the shoulder. It articulates with the clavicle—the sole point of attachment of the arm and scapula to the rest of the skeleton.

2. The coracoid49 (COR-uh-coyd) process is shaped like a finger but named for a vague resemblance to a crow's beak; it provides attachment for the biceps brachii and other muscles of the arm.

49 corac = crow + oid = resembling

49 corac = crow + oid = resembling

Right Clavicle Superior View
Figure 8.30 The Right Clavicle (collarbone). (a) Superior view; (fa) inferior view.

Chapter 8 The Skeletal System 273

3. The glenoid50 (GLEN-oyd) cavity is a shallow socket that articulates with the head of the humerus.

Was this article helpful?

0 0
Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

Get My Free Ebook


Responses

  • david
    How is the unusual flexibility of the human shoulder joint related to the habitat of other primates?
    3 years ago
  • carys
    How is the unusual flexibility of the human shoulder related to the habit of other primates?
    3 years ago
  • mattiesko
    How is the unusual flexibility of a human shoulder joint related to the habitat of other primate?
    3 years ago
  • belladonna grubb
    How is the unusual flexibillity of the human shoulder related to other primates habitat?
    3 years ago

Post a comment