Lab Objectives:

• Remove thoracolumbar deep fascia to expose underlying epaxial muscles.

• Examine the organization of epaxial muscles (three longitudinal systems,
    each system subdivided transversely per region):
      - iliocostalis system (lumborum & thoracis regions)
      - longissimus system (lumborum, thoracis, cervicis, & capitis)
      - transversospinalis system (named muscles, especially large in the neck)

•Identify "two" transversospinalis epaxial muscles in the neck
      - splenius m.
      - semispinalis capitis m. (two parts: biventer cervicis m. & complexus m.)

• In the dog, examine the elastic nuchal ligament, which is a continuation of the collagenous
       supraspinous ligament.

•Reflect skin from the neck and thorax on the right side. Find the following cervical nerves:
      - great auricular n. (and transverse cervical n.)
      - accessory n.
      - vagosympathetic nerve trunk


Anatomical Terms:

Trunk and Neck: epaxial muscles, etc.

        Iliocostalis System
                iliocostalis lumborum mm.
                iliocostalis thoracis mm.
        Longissimus System
                longissimus thoracis et lumborum
                longissimus cervicis
                longissimus capitis
        Transversospinalis System
                splenius m.
                semispinalis capitis m.
                        biventer cervicis m.
                        complexus m.
        supraspinous ligament (absent in cat)
        nuchal ligament (absent in cat)

Neck: nerves & vessels
        second cervical nerve (ventral branch)
                great auricular nerve
                transverse cervical nerve
        external jugular vein [palpate]
        mandibular lymph nodes [palpate]
        medial retropharyngeal lymph node
        superficial cervical lymph nodes [palpate]
        accessory (eleventh) cranial nerve
        ventral branches of cervical nerves 3,4,5
        vagosympathetic nerve trunk

                nucha [Latin] = nape of the neck (nuchal ligament)
                longissimus [Latin] = longest (longissimus system)
                epi- or ep- [Greek.] = on/upon/over (epaxial muscles)
                supra- [Latin] = above (supraspinous ligament)
                auricularis [Latin] = pertaining to the ear (great auricular n.)
                auris [Latin] = ear
                et [Latin] = and (thoracis et lumborum)


Instructor Commentary:

Epaxial muscles (epi = upon & axial = axis) are muscles located dorsally along the spine. They are innervated by dorsal branches of spinal nerves and function to extend the vertebral column. Generally, epaxial musculature consists of fascicles running from one vertebra to neighboring vertebrae. As defined in your Dissection Guide (Fig. 2-81), we will divide epaxial musculature into three longitudinal systems (lateral, intermediate and medial) and further subdivide each system transversely by region. In the neck, the mass of epaxial musculature is greatly increased and we will identify individual muscles there.

The cat lacks nuchal and supraspinous ligaments, perhaps this contributes to its greater flexibility compared to the dog. As you will see, the elastic nuchal ligament is best developed in grazing ungulates who have more need for a passive head-elevation aid.

Spinal nerves innervate muscles and skin via dorsal and ventral regional branches. The dorsal branch gives rise to a dorsal cutaneous nerve and it innervates epaxial mm. The ventral branch gives rise to ventral and/or lateral cutaneous nerves and innervates hypaxial mm.

There are eight bilateral pairs of cervical spinal nerves. The first cervical nerve is small and it does not contribute to cutaneous innervation. Thus, the great auricular n. arises from the second cervical spinal nerve (C-2).


Dissection Steps:

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Show List of Dissection Steps (PDF)


Dissection Videos:


Dissection Images:

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