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Unit 20: Superficial Face and Parotid Region Dissection Instructions: The skin of the face is thin and muscles of facial expression often have attachment to it, therefore, it must be removed carefully. The skin of the eyelids is the thinnest. Make the following incisions as outlined in Figure 18-1. Make a mid-line incision extending from the bottom of the chin to the top of the head (A to B). Make a second incision from the bridge of the nose, around the eyelids C to D). Encircle the mouth with another incision, leaving the mucosa of skin of the lips intact and extend the incision to the ear (E and E to F). Also, encircle the nostrils (G ). The skin from both the face and scalp should be reflected as indicated in Figure 20-1. Fig. 19– 1 Once the skin of the face and scalp is reflected, clean the surface of the parotid gland out to its margin (Plate 23, 25; 7.13). The branches of the facial nerve (Plates 25, 61; 7.7, 7.13, 7.39A, B) which innervate the muscles of facial expression will exit the parotid gland at its margins. Locate the duct of the parotid gland as it leaves the gland at its anterior margin, paralleling the zygomatic arch and lying a fingers breadth below it. It crosses superficial to the masseter muscle and pierces the buccinator muscle to open into the mouth cavity opposite the second upper molar tooth (Plates 25, 61, 72; 7.12,). As the branches of the facial nerve and the parotid duct are cleaned, identify the muscles of facial expression. Identify the orbicularis oculi muscle as it encircles the palpebral fissure. It is used to close the eye (Plates 26, 123; 7.12, Table 7.1 and figures p. 629). Note its orbital and palpebral parts. Identify the orbicularis oris muscle as it encircles the mouth. Observe that a number of other muscles mingle with the orbicularis oris muscle (Plates 26, 123; 7.15, Table 7.1 and figures p. ΗΑ−20−1 629). Locate as many of the following muscles as possible: the levator labii superioris muscle which has three parts, a medial part called the levator labii superioris alaeque nasi, a middle part and a lateral part called the zygomaticus minor; the zygomaticus major muscle which is lateral to the zygomaticus minor muscle; the levator anguli oris muscle which is deep to the above muscles and is useful in smiling; the risorius muscle which has horizontal fibers running from the angle of the mouth and it broadens the smile; the depressor anguli oris which is triangular in shape with its base inferior and its upper angle at the angle of the mouth; the depressor labii inferioris which is deep and medial to the depressor angulae oris muscle; and the mentalis muscle which is deep to the skin of the chin. Locate the buccinator muscle an important muscle of facial expression (Plates 26, 54, 60, 61, 68;7.12, 7.13, Table 7.1 and figures p. 629). Again note the parotid duct piercing the muscle. Observe the platysma muscle, the largest of the muscles of facial expression.. Look again at the branches of the facial nerve. Usually the nerve divides into upper and lower divisions within the substance of the parotid gland (Plates 25, 123; 7.13, 7.39, Table 9.9 and figures p. 830). The upper division has branches which go to the temporal, zygomatic and buccal regions to innervate muscles in those areas. The lower division has branches which go to the cervical, mandibular and buccal regions. The facial nerve also has a posterior auricular branch serving muscles posterior to the ear. The posterior belly of the digastric muscle and the stylohyoid muscle are also innervated by the facial nerve. At the angle of the mandible (Plates 23, 25, 54; 7.41; 7.46), clean the masseter muscle and note its origin from the zygomatic arch and its insertion on the angle and ramus of the mandible. This is a muscle of mastication. Follow its anterior border to the lower border of the mandible and locate the facial artery. Follow the facial artery which is a branch of the external carotid artery onto the face (Plates 23, 36, 69, 85; 7.12, 7.13 8.10, Table 7.3 and figures p. 632). It has named branches to the lower and upper lips, but supplies the entire anterior facial area. At the orbit, it anastomoses with the superficial branches of the ophthalmic artery, thus connecting internal and external carotids. The superior labial artery branches contributes to the circulation of the nasal mucosa. It also anastomoses with the transverse facial branch of the superficial temporal artery, one of the terminal branches of the external carotid. The left and right facial arteries anastomose across the mid-line. Note its relationship to the facial vein. Follow the superficial temporal artery and vein, a terminal branch of the external carotid artery to the side of the head and scalp which it supplies (Plates 23; 7.13, 7.21, Table 7.4 and figure p. 633). These are superficial and anterior to the tragus of the ear, where the pulse of the artery can be felt. The external carotid artery ends deep and posterior to the neck of the mandible. Note the retromandibular vein as it accompanies the external carotid artery. HA-20-2 Carefully pick away the parotid gland on one side of the face to observe the facial nerve, retromandibular vein and carotid arteries (Plates 25, 61, 70, 123; 7.13, 7.39B). Leave some gland tissue on the parotid duct so it can be recognized later, but otherwise remove the entire gland. When it is completely removed, the styloid process, stylohyoid muscle and posterior belly of the digastric muscle should be seen anterior to the mastoid process. Clean and study the sensory innervation of the face. Locate the terminal branches found in the face and scalp of the ophthalmic, maxillary and mandibular divisions of the trigeminal nerve (Plates 24, 36, 45, 71, 122; 7.15, 7.16C Table 7.2 and figures-p. 605 figures p. 631). ΗΑ−20−3 Be sure to identify all of the following in this unit: parotid gland duct of parotid gland facial nerve masseter muscle buccinator muscle frontalis muscle occipitalis muscle galea aponeurotica orbicularis oculi muscle corrugator supercilii muscle orbicularis oris muscle posterior belly of digastric muscle infratrochlear nerve supratrochlear nerve levator anguli muscle risorius muscle depressor anguli oris muscle levator labii superioris muscle zygomaticus major muscle zygomaticus minor muscle mentalis muscle platysma muscle facial artery angular artery superior labial artery superficial temporal artery facial vein retromandibular vein, anterior branch of auriculotemporal nerve styloid process of temporal bone stylohyoid muscle lacrimal nerve dorsal nasal nerve infraorbital nerve zygomaticofacial nerve zygomatico-orbital nerve depressor labii inferioris muscle mentalis muscle levator labii superioris alaeque nasi muscle ΗΑ−20−4