CONTENTS MENU:

 

Lab Objectives:

• On the body surface, identify: umbilicus, mammary glands (teats), and costal arch.

• Incise skin and reflect it from the thorax, neck, and brachium.

• Observe and then remove subcutaneous structures (areolar tissue containing fat & fluid,
   superficial fascia, cutaneous muscles; mammary glands).
   Identify cutaneus trunci m. in the thoracic region.

• Clean and identify 3 of 8 extrinsic mm. of the thoracic limb:
      - superficial pectoral m. (descending and transverse parts)
      - deep pectoral m.
      - brachiocephalicus m. (two divisions; clavicular intersection):
          -- cleidobrachialis m.
          -- cleidocephalicus m. (has two parts):
                  cervical part (formerly named cleidocervicalis)
                  mastoid part (formerly named cleidomastoideus)

 

Anatomical Terms:

Superficial Structures
        umbilicus
        thoracic mammae (cranial & caudal)
        abdominal mammae (cranial & caudal)
        inguinal mammae
        costal arch
        fascia (superficial & deep fascia)
        cutaneous muscle
                cutaneus trunci m.
                preputial muscle (male)
        [Notice: regional differences in skin thickness & foot pads]

Thoracic Limb Extrinsic Muscles
        superficial pectoral muscle
                descending & transverse parts
        deep pectoral muscle
        brachiocephalicus m.
                clavicular intersection (cat: clavicle bone remnant)
                cleidobrachialis m.
                cleidocephalicus m.
                        pars cervicalis (cleidocervicalis m.)
                        pars mastoidea (cleidomastoideus m.)

        Note:
                cutaneous = English adjective pertaining to skin
                cutaneus = Latin adjective [L. cutis = skin] used in: cutaneus trunci m.

 

Instructor Commentary:

After examining the outer surface of the cadaver, incise and reflect skin from the thorax, neck, and brachium. Observe subcutaneous structures. These include: superficial fascia, areolar tissue, cutaneus trunci m, and mammary glands (5 pair in the dog; 4 pair in the car).

A distinction can be made between fascia (highly fibrous) and areolar tissue (less fibrous with pockets for fat and fluid). Fascia and areolar tissue are found together in both superficial (subcutaneous) and deep locations.

A distinction is made between superficial fascia and deep fascia. The latter is found among the muscles and bones of the trunk and limbs. The former occupies the subcutaneous space between deep fascia and the skin. The superficial-deep boundary is often ambiguous.

There are eight extrinsic muscles of the thoracic limb. Extrinsic muscles have one attachment on the limb and one attachment on the trunk or neck/head. Their actions depend on weight distribution. They move the limb relative to the body, but if the limb is anchored by body weight, the body is moved relative to the limb. (In contrast, intrinsic muscles are attached totally to limb bones and thus they move only joints of the limb.) The largest extrinsic limb muscle, the serratus ventralis m., holds the weight of the trunk as it is suspended between the thoracic limbs.

In the neck, the brachiocephalicus m. features a clavicular intersection that separates its cleidobrachialis m. division from its cleidocephalicus m. division, the latter has both cervical and mastoid parts (previously the parts were designated cleidocervicalis m.and cleidomastoideus m.). Mastoid refers to a process (bump) on the temporal bone of the skull.

The term clavicular intersection refers to fibrous tissue (including sometimes fibrocartilage or a sliver of bone) that occupies the position of the clavicle (a bone that anchors the shoulder joint to the sternum in primates and birds). Running animals have evolved a laterally flattened chest and a mobile shoulder, to increase stride length and thus running speed. In the process, they have lost the clavicle as a functional bone.

In the cat, the clavicular intersection consistently contains bone. Also, the pectoral mm. and the cleidobrachialis m. attach more distally on the thoracic limb in the cat, compared to the dog.

 

Dissection Videos:

 

Dissection Images:

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