Prelab Images - Anterior Triangle of the Neck

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 Atlas images listed below.
1. Review the bony landmarks. (Play movie)
Plate 419 shows the clavicle (the superior border is not labeled, but is easy to find). Plate 15 shows the mandible and the mandibular angle, inferior border of mandible (not labeled), and the mental protuberance (mental protuberance also shown in plate 2). The jugular notch is labeled in plates 185 and 1. The mastoid process is in plates 4,8, and 13. The hyoid bone, thyroid cartilage, cricoid cartilage, and trachea are in plates 28, 29, and 77. The laryngeal prominence is the part of the thyroid cartilage that bulges out of the neck anteriorly and is labeled in plate 77 (right lateral view) and can be seen in plate 1 around the area labeled thyroid cartilage. Plate 13 shows a good bony framework of the neck that you may want to refer to.
Step 2. Remove any remaining skin in the neck region and expose the platysma. (Play movie)
Plate 26 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 33 and 129 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 28 and 135 (the nerves with the blue line) show the greater auricular, transverse cervical, lesser occipital, and supraclavicular nerves. Plate 32 (bottom) is a schematic of the cervical plexus from which these nerves come. Plates 35, 36, and 185 should aid you in finding these nerves in your dissection (NOTE: in plate 32 there is an error, the lesser occipital nerve is actually superior to the greater auricular nerve, not inferior to it). Plate 31 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 256, but is not labeled). Plate 74 shows the origin of the external and anterior jugular veins from 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 35. 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 28. 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 28) muscle and then remove it from the clavicle and sternum and reflect it superiorly. Next, clean the sternohyoid and omohyoid muscles (seen in plate 29 top picture, left side of the picture). Plate 31 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 (right half of plate 31). 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 29 and 31 shows the thyrohyoid and sternothyroid muscles. Plates 32 and 129 show branches of the ansa cervicalis innervating these four infrahyoid muscles and that the thyrohyoid receives its innervation (plates 128 and 129) from a part of the ansa cervicalis that travels with the hypoglossal nerve (CN XII). Plate 127 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 32 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 32 and 34 (top). Now open the carotid sheath. Plates 32, 34, and 74 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 126 labels superior, inferior, and thoracic cardiac branches of the vagus nerve, which you may find during this dissection. Plate 226 shows cardiac branches continuing to form the cardiac plexus. Plates 72 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 74 shows the thyroid gland and identifies both of the lobes, the isthmus, and the pyramidal lobe. Plate 31 shows the fascial investment of the thyroid gland. Plates 29 and 74 show its relationship to other structures in the neck. Plate 74 shows the superior thyroid artery and plate 69 shows this artery branching off the external carotid artery. The superior thyroid vein is also shown in plate 74 coming from the internal jugular vein. Plate 74 shows the external branch of the superior laryngeal nerve to the cricothyroid muscle. Plate 78 (right lateral view) gives a better view of the cricothyroid muscle. Plates 75 and 76 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 in plate 74, but in 10% of people it runs up from the aortic arch or brachiocephalic artery to the isthmus of the thyroid gland. Plate 74 shows the middle and inferior thyroid veins. Plate 33 shows the inferior thyroid artery as a branch of the thyrocervical trunk. Plates 74, 75, and 76 show this artery supplying the thyroid gland. Plate 232 shows the right and left recurrent laryngeal nerves branching off the vagus nerve (CN X). Plates 74, 75, and 76 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 78 and 79 (except for the cricothyroid muscle which is supplied by the external branch of the superior laryngeal nerve). Plate 74 reviews the innervation of the larynx. Plate 75 shows the parathyroid glands embedded in the posterior side of the thyroid gland where you will find them in lab (may be attached directly to the inferior thyroid artery).