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Shoulder
Brachium
Antebrachium
Facial
and Masticatory Muscles
Thorax
and Heart
Brain
Body
Wall
Hip
and Thigh
Shank
and Foot
Digestive
System
Urinary
and Reproductive Systems
Hip
and Tail
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 Shoulder
of the Rat (Rattus norvegicus)
Text and Photos by Yu Jin Kim and Ana Panduro
Part I : Surface Anatomy & Dissection
Specimen:
Rattus norvegicus is a quadruped rodent with relatively short
forelimbs and hindlimbs compared to its body length. Its body length
is 20cm and its tail length is 20cm as well so the total length of our
rat from the head to tip of the tail is 40 cm. Our specimen is a female
and overall it did not have any noticeable damage on the surface, but
when the skin was cut and its dorsal neck region was revealed it had been
destroyed so that we could not observe muscles around this area.
Dissection Instruction :
In order to cut off the skin we first made a longitudinal cut on its
dorsal side. Peeling the skin off was difficult in some areas such as
cutaneous maximus because muscles are attached to the skin and it was
hard to separate the muscles from the skin. Other than that most skin
parts peeled off easily and we could see the superficial muscles immediately.
Some of the superficial muscles that we observed were: cutaneous maximus,
platysma, trapezius, sternocleidomastoid, and pectoralis major. The spinotrapezius,
acromiotrapezius and clavotrapezius muscles make up the trapezius muscles
and in our Rattus norvegicus the spinotrapezius was very underdeveloped
and was just a thin, translucent, white strip. In order to have a good
view of the muscles and have good clear pictures, we did some clean-up
to remove hair and the thin layer of fascia between the skin and the underlying
muscles. After identifying all the superficial muscles, we cut the medial
border of the pectoralis superficialis muscle and reflected it in order
to find pectoralis profundus. We also cut latissimus dorsi near the humerus
in order to observe other deep shoulder muscles. Deep shoulder muscles
that we found were: supraspinatus, infraspinatus, teres major, teres minor,
rhomboideus, subscapularis and serratus ventralis.
Part II: Cutaneous features
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origin
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insertion
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action
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platysma
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cervical region and base of ear; lateral cervical region; and
manubrium of the sternum
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orbicularis oculi muscle; fascia of masseter; manubrium of the
sternum
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tenses and moves the skin in the neck and masseter region
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cutaneous maximus/ cutaneous trunci
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axillary region
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skin, (covers the lateral thoracic and abdominal wall from the
shoulder to the root of the tail)
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tenses and moves the skin of the trunk
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Part III: Branchiomeric muscles
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origin
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insertion
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action
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trapezius
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a. spinotrapezius
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spinous processes of vertebrae, from fourth thoracic to third lumbar
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proximal spine of scapula
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fixation of spine of the scapula, lifts and draws the limb ventrally
and dorsally
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b. acromiotrapezius
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spinous processes of vertebrae, from first cervical to fourth thoracic
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acromion process, spine of scapula
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fixation of spine of the scapula, lifts and draws the limb ventrally
and dorsally
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c. clavotrapezius
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superior nuchal line, external occipital protuberance
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posterior border of clavicle
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lifts and draws the limb ventrally and dorsally
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sternomastoideus
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manubrium of the sternum
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mastoid part of the temporal bone
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flexes the head and neck laterally
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cleidomastoideus
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middle part of clavicle
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mastoid process. occipital and temporal ridges
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flexes head and neck
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Part IV: Superficial Shoulder Muscles
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origin
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insertion
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action
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pectoralis
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a. pectoralis profundus
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manubrium of sternum, second sternebra
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distal portion of the deltoid tuberosity
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draws the limb dorsally
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b. pectoralis superficialis
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clavicular part from the sternal third of the clavicle, manubrium,
and first costal cartilage. Transverse part from the second through
sixth costal cartilage and the ventral face of the sternum
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deltoid tuberosity
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adducts limb and draws it dorsally
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latissimus dorsi
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lumbodorsal fascia and spinous processes of the 5th-10th
thoracic vertebrae
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proximal end of the medial humerus
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moves limb dorsally while flexing at the shoulder joint
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levator scapulae ventralis/ Omotransvarsarius
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acromion and hamate processes of the scapular spine
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wing and body of the atlas
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ventral motion of the scapula
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deltoids
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a. clavodeltoid
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clavicle
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deltoid tuberosity of humerus
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rotates the limb medially
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b. acromiodeltoid
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acromion and hamate processes
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deltoid tuberosity of humerus
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abduction, scapular part flexion of shoulder joint
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c. spinodeltoid
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infraspinous fasica, anterior spine of scapula
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deltoid tuberosity of humerus
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flexion of the shoulder joint
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Part V: Deeper Shoulder Muscles
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origin
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insertion
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action
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supraspinatus
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cervical border and supraspinous fossa of the scapula (Caudal head
originates along the scapular spine and from supraspinous fossa)
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greater tubercle of the humerus
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extension of the shoulder joint
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infraspinatus
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spine, thoracic border, and infraspinous fossa of the scapula
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greater tubercle of the humerus
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extension of the shoulder
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teres major
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thoracic angle and proximal part of the caudal border of the scapula
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medial neck of the humerus
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flexion of shoulder
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teres minor
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axillary border of scapula
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greater tubercle of the humerus
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flexion of the shoulder
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rhomboideus
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spinous process of fourth-seventh cervical vertebrae (R. major);
spinous process of first three cervical vertebrae
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medial border of scapula
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elevates the limb
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subscapularis
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subscapular fossa
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lesser tubercle of humerus
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extension of the shoulder
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serratus ventralis
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cervical part from the transverse processes of the second through
eighth cervical vertebrae, thoracic part with serrations from the
middle third of the first 8 ribs
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along the medial side of the dorsal edge of the scapula
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suspension of the trunk between the limbs. When the limbs are fixed
the cervical part raises the neck, the thoracic part elevates the
trunk and draws it forward.
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References:
1. Hebel, Rudolf and Melvin W. Stromberg. 1986. Anatomy and Embryology
of the Laboratory Rat. BioMed Verlang Wörthsee, Germany.
2. Greene, Eunice Chace. 1935. Anatomy of the Rat. The American Philosophical
Society, Philadelphia.
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