Prelab Images - Anterior Triangle of the Neck

Prelab should consist of reading the lab manual and dissector answers and viewing the dissection video. To begin your study, you may find it useful to look over the Netter's or LWW Atlas images listed below.

1. Review the bony landmarks. (Play movie)

Plate N419 or TG7-01 shows the clavicle (the superior border is not labeled, but is easy to find). Plate N15 or TG7-04A shows the mandible and the mandibular angle, inferior border of mandible (not labeled), and the mental protuberance (mental protuberance also shown in plate N2 or TG7-03). The jugular (suprasternal) notch is labeled in plates N185 or TG4-4 and N1 or TG7-01. The mastoid process is in plates N4 or TG7-04A, TG7-05A, N8 or TG7-06, and N13 or TG7-09. The hyoid bone, thyroid cartilage, cricoid cartilage, and trachea are in plates N28 or TG7-12, N29 or TG7-13, and N77 or TG7-25. The laryngeal prominence is the part of the thyroid cartilage that bulges out of the neck anteriorly and is labeled in plate N77 or TG7-01, TG7-26 and can be seen in plate N1, N13 or TG7-09 around the area labeled thyroid cartilage.

Step 2. Remove any remaining skin in the neck region and expose the platysma. (Play movie)

Plate N26 or TG7-11 and TG7-16 shows the skin removed and the large, thin platysma muscle revealed. Make sure to skin very superficially because this muscle is very superficial and it is easily damaged because it is so thin.

Step 3. Reflect the platysma superiorly to expose the cutaneous veins and nerves of the neck. (Play movie)

After cleaning the platysma remove it from its attachment to the clavicle and reflect it upwards towards the mandible careful not to damage the veins and cutaneous nerve underneath it. Plates N33 or TG7-11, TG7-31 or N129 or TG7-87 show the cervical branch of the facial nerve (CN VII), which you may see if you reflect the platysma far enough and look near the angle of the mandible. Plates N28 or TG7-11, TG7-16A , TG7-16B and N135 show the greater auricular, transverse cervical, lesser occipital, and supraclavicular nerves. Plate N32 is a schematic of the cervical plexus from which these nerves come. Plates N35 or TG7-11, N36 or TG7-16A and TG7-16B, and N185 should aid you in finding these nerves in your dissection (NOTE: in plate N32 there is an error, the lesser occipital nerve is actually superior to the greater auricular nerve, not inferior to it). Plate N31 or TG7-11 show the external jugular, anterior jugular, and the communicating vein. The jugular venous arch is formed just above the jugular notch of the sternum by communicating branches between the anterior jugular veins (this is seen in plate N256 or TG7-11). Plate N74 shows the external and anterior jugular veins draining to the subclavian vein. The deep cervical fascia, its (superficial) investing layer, infrahyoid (muscular) portion of fascia, visceral fascia (pretracheal and buccopharyngeal), carotid sheath, and prevertebral fascia are all shown in plate N35 or TG7-10, TG7-11. This is an important figure to be familiar with.

Step 4. Identify the triangles of the neck and clean the strap muscles and reflect them to expose the ansa cervicalis and the thyroid gland. (Play movie)

The triangles of the neck can be seen in plate N28 or TG7-02A, TG7-02B. It may be helpful for you to draw them in. The anterior triangle (bounded by the midline, sternocleidomastoid muscle and lower border of the mandible) is composed of four triangles: the submental triangle (bounded by the hyoid bone, the midline, and the anterior belly of the digastric muscle), the submandibular triangle (bounded by the anterior and posterior bellies of the digastric muscle and the lower border of the mandible), the muscular triangle (bounded by the midline, sternocleidomastoid muscle, and the superior belly of the omohyoid muscle), and the carotid triangle (bounded by the sternocleidomastoid muscle, the posterior belly of the digastric muscle, and the superior belly of the omohyoid muscle). The posterior triangle (boundaries are the sternocleidomastoid, trapezius, and the clavicle) is composed of the omoclavicular/subclavian triangle (boundaries are the clavicle, sternocleidomastoid, and inferior belly of the omohyoid muscle) and the occipital triangle (bounded by the trapezius, sternocleidomastoid, and inferior belly of the omohyoid muscle). Returning to the dissection, clean the sternocleidomastoid (plate N28 or TG7-12) muscle and then remove it from the clavicle and sternum and reflect it superiorly. Next, clean the sternohyoid and omohyoid muscles (seen in plate N29 or TG7-12). Plate N31 or TG7-12 gives a good view of both heads of the omohyoid muscle and the intermediate tendon between the two. Clean the muscles from medial to lateral because they receive their innervation from their lateral borders (N31 or TG7-12). Then cut the sternohyoid from its sternal attachment and reflect it superiorly and cut the omohyoid from its hyoid attachment and reflect it laterally. Plate N29 or TG7-13 and N31 or TG7-13 shows the thyrohyoid and sternothyroid muscles. Plates N32 and N129 or TG7-17 show branches of the ansa cervicalis innervating these four infrahyoid muscles and that the thyrohyoid receives its innervation (plates N128 and N129 or TG7-13) from a part of the ansa cervicalis that travels with the hypoglossal nerve (CN XII). Plate N127 or TG7-17 shows the accessory nerve (CN XI) that innervates the sternocleidomastoid muscle (and trapezius). Cut the sternothyroid muscle from its sternal attachment and reflect it superiorly.

Step 5. Open the carotid sheath to expose the associated vessels and nerves. (Play movie)

Plate N32 or TG7-13, TG7-17 shows the superior root of the ansa cervicalis, vagus nerve (CN X), carotid artery, and internal jugular vein, which will all be in the carotid sheath. The ansa cervicalis can be traced by following branches from the infrahyoid muscles inferiorly back to the cervical plexus and superiorly to the hypoglossal nerve (CN XII) shown in plates N32 and N34 or TG7-13. Now open the carotid sheath. Plates N32, N34 or TG7-13, and N74 or TG7-14 identify the internal jugular vein, common and external carotid arteries, and the vagus nerve (posterior to the carotid artery and internal jugular vein) contained within this sheath. Plate N126 or TG7-92 labels superior, inferior, and thoracic cardiac branches of the vagus nerve, which you may find during this dissection. Plate N226 or TG7-92 shows cardiac branches continuing to form the cardiac plexus. Plates N72 or TG7-74 shows the deep cervical lymph nodes, many of which are along the internal jugular vein.

Step 6. Dissect the thyroid gland, its vascular supply, the recurrent laryngeal nerves and the parathyroid glands. (Play movie)

Plate N74 or TG7-13 shows the thyroid gland and identifies both of the lobes, the isthmus, and the pyramidal lobe. Plate N31 or TG7-11 shows the fascial investment of the thyroid gland. Plates N29 or TG7-13 and N74 or TG7-14 show its relationship to other structures in the neck. Plate N74 or TG7-14 shows the superior thyroid artery and plate N69 or TG7-19 shows this artery branching off the external carotid artery. The superior thyroid vein is also shown in plate N74 or TG7-14 draining to the internal jugular vein. Plate N74 or TG7-18 shows the external branch of the superior laryngeal nerve to the cricothyroid muscle. Plate N78 or TG7-26 gives a better view of the cricothyroid muscle. Plates N75 or TG7-21 and N76 show external branch of the superior laryngeal nerve from a posterior view running near the superior thyroid artery and innervating the inferior pharyngeal constrictor muscle before moving to the front of the larynx to innervate the cricothyroid muscle. Next cut through the isthmus of the thyroid and reflect the lobes laterally. The thyroidea ima artery is not pictured, but in 10% of people it runs up from the aortic arch or brachiocephalic artery to the isthmus of the thyroid gland. Plate N74 or TG7-13 shows the middle and inferior thyroid veins. Plate N33 or TG7-15 shows the inferior thyroid artery as a branch of the thyrocervical trunk. Plates N74, N75 or TG7-15, and 76 or TG7-14 show this artery supplying the thyroid gland. Plate N232 or TG4-38 shows the right and left recurrent laryngeal nerves branching off the vagus nerve (CN X). Plates N74, N75 or TG7-19, and N76 show the recurrent laryngeal nerve running in the tracheoesophageal groove (groove between the trachea and the esophagus). It will end up supplying the muscles of the larynx in plates N78 or TG7-26 and N79 (except for the cricothyroid muscle which is supplied by the external branch of the superior laryngeal nerve). Plate N74 or TG7-26 reviews the innervation of the larynx. Plate N75 or TG7-14 shows the parathyroid glands along the posterior side of the thyroid gland where you will find them in lab (may be attached directly to the inferior thyroid artery).