TERCER TRIMESTRE
H. Concreciones metodológicas
The superficial facial muscles in the masseteric and temporal regions will be dissected on the left half of the head and the mandibular muscles will be demonstrated on the right half of the head, where the skin is removed. The innervation by the mandibular nerve (V3) will be identified later after the removal of the mandible (see page 97).
1
2
95
5
27 26
20 25
1 2
4 3 22 Regions of face
Frontal region
Masseteric and temporal regions
Legend :
Muscles of head
1 Levator nasolabialis m.
2 Orbicularis oculi m.
3 Retractor anguli oculi lat. m.
4 Frontoscutularis m.
5 Orbicularis oris m.
6 Malaris m.
7 Zygomaticus m.
8 Parotidoauricularis m.
supf. m.
10 Scutuloauricularis 9 Cervicoauricularis supf. m.
11 Scutiform cartilage
12 Cervicoscutularis m.
13 Occipitalis m.
14 Interscutularis m. 16 Temporalis m.:
Supf. tendon Principal part
Accessory part
15 Levator anguli oculi med. m.
17 Buccinator m.
18 Mylohyoideus m.
19 Masseter m.
20 Digastricus m.
21 Zygomaticoauricularis m.
Platysma:
22 Cutaneus colli m.
23 Cutaneus faciei m.
24 Sphincter colli supf. m.
25 Orbital lig.
26 Mandibuloauricularis m.
27 Stylohyoideus m.
(see pp. 93, 97)
24 23
22 21
96
a) The INTERNTAL MUSCLES OF MASTICATION include the strong m. ptery-goideus medialis and the weak m. pteryptery-goideus lateralis. They extend from the pterygoid and adjacent bones to the indistinct pterygoid fossa on the medial surface of the ramus of the mandible. The mm. pterygoideus medi-alis and pterygoideus latermedi-alis are innervated by the deeply situated nerves of like name. They leave the mandibular n. (V3) immediately after its emer-gence from the foramen ovale.
The origin of the m. pterygoideus medialis (8) exhibits a conspicuous, glis-tening tendon on its external surface and is crossed superficially by the mandibular n.
The m. pterygoideus lateralis (18) is significantly smaller. It lies dorsal to the caudal border of the medial muscle, in the bifurcation between the buc-cal n. and the parent mandibular n.
b) The TRIGEMINALN. (V; see also text-illustration) has a large sensory root and a smaller motor root. After leaving the brain but before passing through the skull, the sensory fibers of the large root are associated with the trigeminal ganglion (see p. 137). At the ganglion, the peripheral processes of the nerve cells form the three branches of the trigeminal n. The first branch, the sensory ophthalmic n. (V1), passes through the orbital fis-sure. The second branch, the sensory maxillary n. (V2), passes from the alar canal to ramify in the pterygopalatine fossa. The third branch, the mandibular n. (V3), joins the motor root before passing through the fora-men ovale.
I. The mandibular n. (V3, —5) passes from the foramen ovale medial to the temporomandibular articulation and gives off the following nerve branch-es:
The n. masticatorius (4) supplies purely motor branches, the deep tempo-ral nn. and the masseteric n. (see p. 95), to the like-named muscles of mas-tication.
With the n. masticatorius, the buccal n. (1) passes rostrodorsolaterally over the m. pterygoideus lateralis. Its sensory fibers supply the oral mucous membrane, and its autonomic fibers pass to the zygomatic and buccal glands.
The lingual n. (10) is the direct continuation of the mandibular n. The chor-da tympani of the facial nerve passes rostroventrally from the tympanic fis-sure, crosses the external carotid artery medially and joins the commence-ment of the lingual n. at an acute angle. The special sensory fibers of the chorda tympani supply the taste buds of the rostral two-thirds of the tongue. Its autonomic fibers reach the mandibular gland and, rostrally, the sublingual gland. Sensory fibers of the lingual n. supply the rostral two-thirds of the tongue. A branch, the sublingual n. (11), supplies the mucosa of the floor of the mouth.
The auriculotemporal n. (7) branches near the emergence of the mandibu-lar n. from the foramen ovale and runs caudally around the temporo-mandibular articulation in a ventrally convex arch. Its autonomic fibers supply the parotid gland, and a sensory branch, the n. of the external acoustic meatus, supplies the meatus as far as the tympanic membrane. Its sensory rostral auricular branches pass on the rostral border of the exter-nal ear, and its sensory transverse facial branch supplies the face.
The mylohyoid n. (9) supplies motor innervation to the mylohyoideus mus-cle and the rostral belly of the m. digastricus; whereas, its sensory sub-mental branches ramify in the chin region.
The inferior alveolar n. (6) enters the mandibular canal at the mandibular foramen (where it was previously transected). Here, it provides sensory fibers to the teeth of the lower jaw, and the skin of the chin by way of the mental branches that emerge through mental foramina.
II. The maxillary n. (V2, —16) passes through the foramen rotundum (round foramen) into the alar canal. This purely sensory nerve ramifies with three main nerve branches:
The zygomatic n. (14) proceeds to the ocular bulb and bifurcates within the periorbita into a ventral zygomaticofacial ramus (13) and a dorsal zygo-maticotemporal ramus (12). The latter receives autonomic fibers from the pterygopalatine ganglion and conveys these to the lacrimal gland. After leaving the orbit both rami supply the skin of the face dorsolateral to the eye.
The infraorbital n. (15), a sensory nerve, continues the rostral course of the maxillary n. and, in the pterygopalatine fossa, enters into the infraorbital canal through the maxillary foramen. Within the pterygopalatine fossa it gives off alveolar branches that enter alveolar foramina of the maxilla to reach the caudal cheek teeth, and within the infraorbital canal it supplies branches to the remaining teeth of the upper jaw. After leaving the infra-orbital foramen, the infrainfra-orbital nerve furnishes sensory branches to the external nose and the upper lip.
The pterygopalatine n. (17) leaves the maxillary n. rostrovenrally. On its dorsal border, medial to the infraorbital n., the pterygopalatine n. exhibits the brownish pterygopalatine ganglion (m). This ganglion receives its parasympathetic and sympathetic fibers from the slender nerve of the pterygoid canal from VII and the sympathetic trunk respectively. The parasympathetic fibers synapse here with second neurons of the ganglion, and from the ganglion both sympathetic (without synapse) and parasym-pathetic fibers then pass to the end-branches of the pterygopalatine nerve.
The following three end-branches, in dorsoventral sequence, supply senso-ry fibers to the mucous membrane and autonomic fibers to the glands of their area of supply, the palatine and nasal glands:
The caudal nasal n. (21) passes through the sphenopalatine foramen to the lateral nasal gland and the nasal conchae.
The greater palatine n. (20) reaches the hard palate through the greater palatine canal.
The lesser palatine n. (19) extends rostroventrally and medially around the rostal border of the medial pterygoid muscle to reach the soft palate.
5. Internal (Depp) Muscles of Mastication, Trigeminal Nerve (V), Maxillary Nerve (V2) and Mandibular Nerve (V3)
The head is bisected midsagittally. The right half is used for the present dissection and involves the disarticulation of the right side of the mandible and subsequent demonstration of internal muscles of mastication, and the mandibular and maxillary nn. The masseter muscle is removed in layers so that one is able to observe the different fiber directions of the superficial and deep parts of the muscle and its strong central tendons. Two centimeters rostral to the temporomandibular articulation, the terminal branches of the masseteric n. (3) are then demonstrated on the cut surface of the muscle after the nerve courses laterally over the mandibular notch. The zygomatic arch is sawn through at the temporomandibular articulation and rostral to the attachment of the orbital ligament. The isolated piece of arch is then removed. The m. digastricus is detached at its insertion onto the ventral border of the body of the mandible, taking care to preserve the branch of the mylohyoid n. innervating it. Subsequently the m. mylohyoideus is incised at its origin along the mylo-hyoid line in common with the oral mucous membrane lying deeper. With a strong sideways movement of the mandible it is possible to transect: a) the insertion of the m. temporalis onto the medial and lateral surfaces of the coronoid process of the mandible; and b) the mm. pterygoideus medialis and lat-eralis at the pterygoid fossa. Following this, the inferior alveolar a., v., and n. are cut through at the mandibular foramen, the entrance to the mandibular canal. The preparation is completed by disarticulating the mandible after transecting associated ligaments. The articular cavity is subdivided into two
‘storeys’ by the articular disc. To widen the field of dissection, the m. temporalis is removed in part as far as the dorsal contour of the periorbita. The deep temporal nn. (2) within the m. temporalis are preserved and followed retrogressively to their ramification from the masticatorius n. in common with the masseteric n. To demonstrate the branches of the maxillary n., the zygomatic gland is retracted from the pterygopalatine fossa.
1
2
3
7
2
3 V1 4
V3 V2
14 21
15
17 20 19
10 1
6
9 11
f 10
Trigeminal n. (V)
Ethmoidal n.
Nasociliary n. Long ciliary nn.
Lacrimal n.
Infratrochlear n.
Frontal n.
97
28 n
27
15 25
l n
8 41
22 24
26
23
25 g
12 h 14
13
16 15 i
e 18
d
29
f j
b c 33 a
30 32
31
34 36 35
37 k
38
39 40
Legend :
Mandibular n. (V3), maxillary n. (V2), salivary glands
11 Sublingual n.
10 Lingual n.9 Mylohyoid n.8 Pterygoideus med. m.
7 Auriculotemporal n.
6 Inferior alveolar n.
5 Mandibular n. (V3) 4 Masticatorius n.
3 Masseteric n.
2 Deep temporal nn.
1 Buccal n.
(lateral view)
21 Caud. nasal n.
20 Greater palatine n.
19 Lesser palatine n.
18 Pterygoideus lat. m.
17 Pterygopalatine n.
16 Maxillary n. (V2) 15 Infraorbital n.
14 Zygomatic n.
13 Zygomaticofacial br.
12 Zygomaticotemporal br.
22 Auricle (Scapha) 23 Auricular cartilage 24 Frontascutularis m.
25 Temporalis m.
26 Orbital lig.
27 Periorbita 28 Infraorbital for.
29 Parotid papilla
30 Sternothyreoideus m.
31 Sternohyoideus m.
32 Thyreohyoideus m.
33 Hyopharyngeus m.
34 Stylohyoideus m.
35 Hyoglossus m.
36 Digastricus m.
37 Mylohyoideus m.
38 Tongue 39 Frenulum
40 Sublingual caruncle 41 Rostral alar foramen
(see pp. 95, 99, 105)
a Med. retropharyngeal ln.
b Mandibular gl. and duct c Monostomatic sublingual
gl. and duct
d Parotid gland and duct e Parotid ln.
f Chorda tympani g Lacrimal gl.
h Supf. gl. of third eyelid i Zygomatic gl. and duct j Buccal gll.
k Polystomatic sublingual gl.
l N. of pterygoid canal m Pterygopalatine ggl. and
orbital branches
n Superior alveolar branches
D
F E
G H
I
98
b) The OPTIC N. (II, —13) consists of a large bundle of nerve fibers that begins at the retina and the fibers of which, proceeding from the eyeball, receive medullary sheaths. The nerve passes to the optic chiasm, where the optic tract, the continuation to the diencephalon, begins. Developmentally, the optic nerve is to be regarded as a part of the brain. It is surrounded by a continuation of the three meninges, and the myelin sheaths of its fibers are formed by glial cells (oligodendroglia) of the central nervous system.
c) The OPHTHALMICN. (V1, see text-illustration p.96) is the first branch of the trigeminal n. (V). Its branches are the lacrimal, frontal and nasociliary nerves.
The lacrimal n. (5) is slender; it accompanies the artery of like name and the previously discussed ramus zygomaticotemporalis (V2). Its autonomic fibers, which pass from the pterygopalatine ganglion, supply the lacrimal gland; and its sensory fibers, the upper eyelid.
The frontal n. (4) leaves the orbit lateral to the trochlea. It supplies senso-ry innervation to the skin of the frontal region.
The nasociliary n. (10) branches into the infratrochlear, ethmoidal and long ciliary nerves. The infratrochlear n. (22) leaves the orbit ventromedial to the trochlea and supplies the skin at the medial angle of the eye. The eth-moidal n. (8) contains sensory and autonomic fibers. It passes through the ethmoidal foramen (and is most easily identified here in the dissection) and then through the lamina cribrosa to the fundus of the nasal cavity. It can be followed between the m. rectus medialis and the m. obliquus dorsalis to its origin from the nasociliary n. Likewise, the long ciliary nn. (9) branch here from the nasociliary n. and accompany the optic n. laterally. Their sympa-thetic fibers innervate the m. dilatator pupillae and their sensory fibers sup-ply the cornea.
d) The NERVES AND MUSCLES OF THE EYE are discussed together. In the ongoing dissection, the nerves to the extrinsic eye muscles (III, IV and VI) are used to identify the muscles themselves and the nerves are also followed
in retrograde fashion to their origins. The muscles of the ocular bulb (eye-ball) include the mm. rectus dorsalis, —medialis, —ventralis, and –lateralis, the mm. obliquus dorsalis and –ventralis, the m. levator palpebrae superi-oris; and the m. retractor bulbi, which surrounds the optic n. like a cloak.
In the main, the rectus muscles move the eyeball medially toward the nose or laterally toward the temporal region, as well as dorsally and ventrally.
The mm. obliquus dorsalis and ventralis produce inward and outward rotation of the bulb respectively.
I. The oculomotor n. (III) innervates all extrinsic muscles of the eye except the mm. obliquus dorsalis and rectus lateralis. (Some authors exclude the retractor bulbi muscle.)
II. The trochlear n. (IV) supplies only the m. obliquus dorsalis.
III. The abducent n. (VI) innervates the m. rectus lateralis and the lateral portion of the m. retractor bulbi. (Some authors include the entire retrac-tor bulbi muscle.)
The oculomotor n. terminates with its ventral ramus (12) passing distally into the m. obliquus ventralis (23). The ramus can be followed in retro-grade fashion between the mm. rectus lateralis and ventralis and finally through the m. retractor bulbi to the lateral aspect of the optic n. The cil-iary ganglion (15) can be seen there as a brownish body the size of a millet seed. Fine short ciliary nn. from the ganglion accompany the optic n. and penetrate the sclera. They supply parasympathetic fibers to the mm. ciliaris and sphincter pupillae and sympathetic fibers to the m. dilatator pupillae.
The dorsal ramus (11) of the oculomotor n. innervates the m. rectus dor-salis (3) and the more superficial m. levator palpebrae superioris (2), both of which are crossed over in succession by the frontal n. (from V1). The trochlear n. (6) enters the m. obliquus dorsalis (1) at the junction of its cau-dal and middle thirds. The tendon of insertion of the latter muscle passes over the trochlear cartilage, turning here from a longitudinal to a trans-verse direction and ending on the eyeball ventral to the insertion of the m.
rectus dorsalis. The m. rectus medialis (14), which lies ventromedial to the dorsal rectus, is supplied by the oculomotor n. The m. rectus lateralis (24), an abductor of the eyeball (turns the anterior pole of the eyeball laterally), is entered on its dorsal border by the abducens n. (7).
e) The EXTERNAL NOSE (see text-illustration) extends from the root of the nose (D) over the dorsum nasi (E) up to the apex of the nose (G). At the apex, each of the nares is bounded laterally by the wing of the nostril (H,
—ala nasi) and medially by the planum nasale (F). These rostral features are supported by the cartilages of nose and septum. The planum nasale is formed by hairless, modified skin in the region of the nares and exhibits a median philtrum (I). The nasal septum is membranous in the region of the nares and cartilaginous in its rostral two-thirds and supported by bone in its caudal third.
6. Lacrimal Apparatus, Optic Nerve (II), Ophthalmic Nerve (V1), Nerves and Muscles of the Eye, and External Nose
With the separation of upper and lower eyelids, parts of the lacrimal apparatus are exposed as a result. Following this, the apex of the triangular cartilage supporting the third eyelid is freed from its site of attachment in the orbital cavity. On the lateral surface of the cartilage, the cutaneous covering is removed to expose the accessory lacrimal glands, namely the superficial gland of the third eyelid, while numerous lymph nodules are observed on the medial sur-face of the third eyelid. To expose and dissect the ocular bulb, more of the m. temporalis is ablated, the remaining periorbita removed, and the cone of eye muscles retracted ventrolaterally away from the osseous part of the orbital cavity. At this stage, one can see the trochlea (21) dorsomedial to the ocu-lar bulb and should detach it from its site of attachment to the orbit. The optic n. lies centrally in the cone of extrinsic eye muscles and is surveyed by retracting them.
a) The LACRIMALAPPARATUS (see also text-illustration) includes the lacrimal glands and their system of excretory ducts. The lacrimal gland (16), which lies medial to the orbital ligament and the superficial gland of the third eye-lid (20) secrete the lacrimal fluid. This flows from the glands through nar-row ductules into the superior conjunctival fornix (A) of the conjunctival sac. With movement of the eyelids, the cornea is moistened by a film of lacrimal fluid. This collects within the depth of the medial angle of the eye at the lacrimal lake (B) in the middle of which is the lacrimal caruncle (C) appearing above the surrounding fluid. A few millimeters away from the medial angle of the eye, the lacrimal puncta (17) lie near a margin of pig-mented epithelium on the bulbar surface of the upper and lower eyelids.
Lacrimal fluid flows through these small openings to superior and inferior lacrimal canaliculi (18), which, in turn, unite at the lacrimal sac (19). The nasolacrimal duct, which begins here, lies at first in the osseous lacrimal canal and then more rostrally in the lacrimal groove of the maxilla. The duct conveys the lacrimal fluid to the nasolacrimal ostium, a millimeter-sized opening in the nasal vestibule about one centimeter caudal to the ven-tral angle of the naris. The opening is found one centimeter caudal to the ventral angle of the naris at the beginning of the ventral nasal meatus where a distinct pigmented border is visible.
1
2
3
4
A
17 BC
17
99
25
26
27
c b a
d 28
e 30
f 29
31
26
22
35
32 a
28 b
33
f g
i h 34
36 12
f
m l
j k
29 37
24 7 5
6
4
n 2
22 1
21
35
35 24
36
22
38 39 40 41
23
38 39 24
41 40
23 36
3 21
1
14
Legend :
Legend :
Lacrimal apparatus, accessory organs of eye and cranial nn. II, III, IV, V1, V2 and VI
25 Frontoscutularis m.
26 Temporalis m.
27 Orbital lig.
28 Periorbita 29 Maxilla 30 Straight fold 31 Alar fold
32 Rostr. alar foramen 33 Pterygoideus lat. m.
34 Pterygoideus med. m.
35 Retractor bulbi m.
36 Rectus ventr. m.
37 Zygomatic bone 38 Pupil
39 Iris 40 Sclera
41 Tunica conjunctiva of bulb
(lateral view)
(dorsolateral view) 16 Lacrimal gl.
17 Lacrimal punctom 18 Lacrimal canaliculus 19 Lacrimal sac
20 Supf. gl. of third eyelid
15 Ciliary ggl.
14 Rectus med. m.
13 Optic n. (II) 12 Ventral br.
11 Dorsal br.
Oculomotor n. (III) 10 Nasociliary n.
9 Long ciliary nn.
8 Ethmoidal n.
7 Abducens n. (VI) 6 Trochlear n. (IV) 5 Lacrimal n.
4 Frontal n.
3 Rectus dors. m.
superioris m.
2 Levator palpebrae 1 Obliquus dors. m.
(dorsolateral view)
24 Rectus lat. m.
23 Obliquus ventr. m.
22 Infratrochlear n.
21 Trochlea
(rostral view)
(see pp. 97, 103, 105)
a Maxillary n. (V2) b Zygomatic n.
c Zygomaticotemporal br.
d Zygomaticofacial br.
e Nasolacrimal duct
f Infraorbital n.
g N. of pterygoid canal h Pterygopalatine n.
i Pterygopalatine ggl. and orbital brr.
j Superior alveolar brr.
k Caud. nasal n.
l Greater palatine n.
m Lesser palatine n.
n Short ciliary nn.
100
a) NOSE:
I. The nasal cavity begins at the naris with the nasal vestibule (1), which is covered by a pigmented cutaneous mucous membrane. The vestibule hous-es the straight fold (4) dorsally, a mucosal fold extending rostrally from the dorsal nasal concha; the alar fold (3) a cartilage-supported mucosal fold extending rostrally from the ventral nasal concha; and an indistinct basal fold (2) ventral to the alar fold. The nasal cavity proper is covered with res-piratory mucous membrane and contains the dorsal and ventral nasal con-chae (see p. 90). The middle nasal concha coming from the caudal part of the nasal cavity inserts between them. The lateral nasal gland lies in the maxillary recess of the maxilla and, like the nasolacrimal duct, opens into the nasal vestibule. Both the secretion from the gland and the lacrimal flu-id moisten the planum nasale. The fundus nasi (9) houses the ethmoflu-idal labyrinth which is in part clothed with olfactory mucous membrane.
II. Four nasal meatuses extend through the nasal cavity. The dorsal nasal meatus (8) is between the dorsal nasal concha and the nasal bone and leads to the olfactory organ (therefore, the olfactory meatus). The middle nasal meatus (6) first lies between the dorsal and ventral nasal conchae and then, at the middle nasal concha, splits into a dorsal passage and a ventral pas-sage that lead to paranasal sinuses. Hence it is also called the sinus meatus.
The ventral nasal meatus (5) is also called the respiratory meatus. It lies between the ventral nasal concha and the palate and reaches to the fundus nasi where it is continued by the nasopharyngeal meatus to the choanae.
Olfactory, sinus and respiratory meatuses merge medially into the common nasal meatus (7), which is the narrow passage alongside the nasal septum the entire dorsoventral extent of the nasal cavity.
III. The olfactory organ lies in the fundus nasi, its olfactory mucous mem-brane clothing here part of the ethmoidal labyrinth.
IV. The vomeronasal organ (see p. 123) is also lined with olfactory mucous membrane. It is on the floor of the nasal vestibule at the transition to the nasal cavity proper and lies directly on the cartilaginous nasal septum. It communicates with the roof of the oral cavity through the incisive (or nasopalatine) duct. Functionally it serves as an oral olfactory- or
IV. The vomeronasal organ (see p. 123) is also lined with olfactory mucous membrane. It is on the floor of the nasal vestibule at the transition to the nasal cavity proper and lies directly on the cartilaginous nasal septum. It communicates with the roof of the oral cavity through the incisive (or nasopalatine) duct. Functionally it serves as an oral olfactory- or