Lateral View (norma lateralis ï¿½ Fig 319)
When the skull, minus the mandible, is examined from the side, it will be found that the anterior, superior and posterior parts have already been described in the norma frontalis, verticalis and occipitalis respectively. The central area, however, presents many important features which have not yet been described. It is limited above by the temporal line, which corresponds to the peripheral limit of the origin of the temporalis muscle. This line arches upwards and backwards from the zygomatic process of the frontal bone across the coronal suture to the parietal bone. Salient at first, it can be felt easily through the skin, but as it arches across the parietal bone it is much less distinct and is usually represented by two curved ridges, which enclose between them a smooth and often polished strip of bone. Posteriorly the upper of these two lines fades away, but the lower becomes more prominent as it curves downwards and forwards across the squamous part of the temporal bone, just above its union with the mastoid portion. This part of the line, which is termed the supramastoid crest, becomes continuous with the posterior root of the zygomatic process. Throughout the whole of its extent the temporal line marks the periphery of the temporalis muscle and its covering fascia. On the parietal bone the muscle arises from the lower ridge, while the fascia is attached to the upper ridge and the bone below.
The temporal fossa is the region bounded by the zygomatic arch, the temporal line and the frontal process of the zygomatic bone, and its floor gives origin to the temporalis muscle. An irregularly H-shaped arrangement of sutures can be seen in the anterior part of the fossa, the more or less horizontal limb of the H being formed by the suture between the antero-inferior part of the parietal and the upper border of the greater wing of the sphenoid bone. In this situation the frontal, the sphenoid, the parietal and the squamous part of the temporal bone closely adjoin one another (fig. 319), and a small circular area can be outlined so as to include portions of all four. This area is termed the pterion, and its centre–which is an important landmark for the surgeon–lies 3-5 cm. behind and 1.5 cm. above the frontozygomatic suture. The anterior wall of the fossa is formed by the posterior aspect of the upper part of the zygomatic bone, the adjoining part of the greater wing of the sphenoid and a small portion of the frontal bone. It is interposed between the fossa and the orbit. Inferiorly the fossa communicates freely with the infratemporal fossa through the gap which separates the zygomatic arch from the rest of the skull. In this situation the tendon and some fleshy fibres of the temporalis descend to reach their insertion into the mandible.
The zygomatic arch, which is formed by the temporal process of the zygomatic bone and the zygomatic process of the temporal bone, is easily felt through the skin where the cheek and the region of the temple meet each other. Its sharp upper border is obscured by the attachment of the temporal fascia, and its lower border by the origin of the masseter muscle, which arises also from its deep surface. The arch stands away from the rest of the skull and is separated from it by a gap which is deeper in front than behind. Anteriorly, the arch is crossed by the zygomaticotemporal suture, which is directed obliquely downwards and backwards.
The zygomatic process of the temporal bone, or zygoma, widens posteriorly as it approaches the squamous part, and divides into an anterior and a posterior root. The anterior root passes medially in front of the articular fossa for the head of the mandible and becomes continuous with the rounded articular eminence, which forms the anterior boundary of the fossa. The posterior root passes backwards, lateral to the fossa, and its upper border becomes continuous with the supramastoid crest of the temporal bone.
Behind the meatus the lateral aspect of the skull is formed by the mastoid portion of the temporal bone. Above, it is continuous with the squamous portion in front, but behind it possesses a free upper border which articulates with the postero-inferior part of the parictal bone at the horizontal parietomastoid suture. Its posterior border is free and articulates with the squamous part of the occipital bone at the vertical occapitomastoid suture. These two sutures meet each other at the lateral extremity of the lambdoid suture. The mastoid process (fig. 319) is a strong, nipple-shaped projection from the lateral surface of the mastoid portion of the temporal bone. It lies immediately behind the external auditory meatus, projecting downwards to a lower level, and its anterior part can be felt through the skin under cover of the lobule of the auricle. The mastoid foramen pierces the bone opposite the base of the mastoid process and near the occipitomastoid suture ; it transmits an important emissary vein from the sigmoid sinus.
The infratemporal fossa (fig. 320) is an irregularly shaped space which lies behind the posterior surface of the maxilla. It communicates with the temporal fossa above through the gap between the zygomatic arch and the side of the skull. Medial to this gap, the roof is formed by the infratemporal surface of the greater wing of the sphenoid, and a small part of the squamous temporal. In this situation the greater wing is pierced by the foramen ovale and the foramen spinosum. The medial wall is formed, by the lateral pterygoid plate. These walls are considered in detail in connection with the norma basalis. Behind, below and on the lateral side the fossa is freely open. The anterior and medial walls are in contact below but they are separated above by the pterygomaxillary fissure, through which the infratemporal fossa communicates with the small pterygopalatine fossa. The upper end of the pterygomaxillary fissure is continuous with the posterior end of the inferior orbital fissure, which lies between the upper part of the posterior surface of the maxilla and the greater wing of the sphenoid. This fissure connects the infratemporal fossa with the orbit and transmits the maxillary nerve and an important venous connection between the inferior ophthalmic vein and the pterygoid venous plexus.
The pterygopalatine fossa is a small pyramidal space situated below the apex of the orbit. It communicates with the infratemporal fossa through the pterygomaxillary fissure and with the orbit through the posterior end of the inferior orbital fissure. The foramen rotundurrn opens on its posterior wall, and the maxillary nerve, which runs forwards and laterally from the foramen across the upper part of the fossa, is the most important of its contents.
Particular features.-The floor of the temporal fossa is marked by a few sinall vascular furrows, of which the most constant lie above the external auditory meatus and are produced by the middle temporal vessels. In the anterior wall of the fossa the small zygomaticotemporal foramen pierces the temporal surface of the zygomatic bone in an upward and backward direction. It transmits the zygomaticotemporal nerve and a minute artery. In addition to the tendon of the temporalis muscle, the deep temporal vessels and nerves traverse the gala between the zygomatic arch and the rest of the skull and ascend into the temporal fossa.
As the anterior root of the zygoma springs from the process, it is marked by a small tubercle, termed the tubercle of the root of the zygoma. It gives attachment to fibres of the temporomandibular ligament (fig. 508) and can be felt through the skin just in front of the head of the mandible. Behind the articular fossa a small downward projection from the posterior root of the zygoma (sometimes termed the post-glenoid tubercle) meets the tyinpanic plate at the anterosuperior part of the orifice of the external auditory meatus. and its anterior aspect takes a small part in the formation of the articular fossa.
The posterior part of the mastoid process and its rounded apex are roughened by the insertions of the sternomastoid, splenius capitis and longissimus capitis muscles, in that order from before backwards. Just in front of, and parallel to, this roughened area, the partially obliterated remains of the squamomastoid suture may be visible. From the position of the suture it will be obvious that the floor of the suprameatal triangle, and therefore the lateral wall of the tyinyanic antrum, is formed by the squamous part of the tem poral bone. The tympanomastoid fissure is placed on the anterior aspect of the process. The outer opening of the mastoid canaliculus, which transmits the auricular branch of the vagus nerve, is placed between the lips of the fissure.
The styloid process is covered on its lateral aspect by the parotid gland and intervenes between that structure and the internal jugular vein. It gives origin to three muscles. The stylohyoid arises by a delicate tendon from its posterior aspect, about midway between the tip and the base ; the styloglossus from the tip and the adjacent part of the an terior aspect ; and the stylopharyngeus from the medial aspect of the base. The stylomandibular ligament is attached to the lateral aspect of the process in its lower part and the stylohyoid ligament to its tip. Behind the base of the process the facial. nerve emerges from the stylomastoid foramen and passes forwards lateral to the process in the substance of the parotid gland.
The infratemporal fossa (fig. 320) contains the lower part of the temporalis muscle as it passes to be inserted into the coronoid process. The maxillary (internal maxillary) artery and its branches and the pterygoid plexus of veins lie deep to the temporalis in relation to the lower head of the lateral pterygoid muscle. The deepest part of the fossa is occupied by the medial pterygoid muscle, the mandibular nerve and the chorda, tympani. The mandibular nerve enters the fossa through the foramen ovale in its roof and breaks up into its terminal branches under cover of the lateral pterygoid muscle. Its branches traverse the fossa and most of them leave it to gain other regions. The chorda tympani enters the fossa on the medial side of the spine of the sphenoid and runs downwards and forwards to join the lingual nerve before it emerges at the lower border of the lateral pterygoid muscle. The maxillary nerve appears at the upper part of the fossa as it passes from the upper end of the pterygomaxillary fissure to the inferior orbital fissure. The anterior wall of the fossa is pierced by two or three small foramina which transmit the posterior superior dental (alveolar) vessels and nerves. It is limited below by the alveolar part of the maxilla in the region of the molar teeth, and in this situation a horizontal strip of the borne is closely covered with the mucous membrane of the gum. Immediately above this strip the bone gives origin to the upper fibres of the buccinator muscle, which extends backwards behind the last molar tooth on to the tuberosity of the maxilla. The medial wall of the fossa,, formed by the lateral. pterygoid plate, is completed below and in front by the tubercle (pyramidal process) of the palatine bone, which is wedged in between the tuberosity of the maxilla and the lateral pterygoid plate. The superficial head oï¿½ the medial pterygoid muscle arises from this surface of the palatine tubercle and the adjoining part of the maxillary tuberosity.
The pterygomaxillary fissure is a triangular interval formed by the divergence of the maxilla from the pterygoid process of the sphenoid bone. It transmits the terminal part of the maxillary (internal maxillary) artery to the pterygopalatine fossa, and. its uppermost part gives passage to the maxillary nerve, which appears for a very short part of its course in the upper part of the infratemporal fossa before it enters the inferior orbital fissure. The inferior orbital fissure leads forwards into the orbit. Its lower border is marked by a notch which lodges the maxillary nerve and forms the posterior end of the infra-orbital groove.
The pterygopalatine fossa (fig. 321) is bounded above by the inferior surface of the body of the sphenoid and the orbital process of the palatine bone on the medial side, but, laterally it communicates with the orbit through the posterior end of the inferior orbital fissure. It is bounded behind by the root of the pterygoid process and the adjoining part of the anterior surface of the greater airing of the sphenoid ; medially, by the upper part of the perpendicular plate of the palatine bone with its orbital and sphenoidal processes ; in front, by the upper part of the posterior surface of the maxilla. Laterally it communicates with the infratemporal fossa through the pterygomaxillary fissure, and below its anterior and posterior walls come into apposition. The fossa contains the maxillary nerve, the spbenopalatine ganglion and the terminal part of the maxillary (internal maxillary) artery. In addition to the pterygomaxillary and inferior orbital fissures five openings lead to or from the fossa. Of these, three are situated on the posterior wall, viz. the foramen rotundum, the pterygoid canal and the palatinovaginal (pharyngeal) canal, in that order downwards and medially. The foramen rotundion transmits the maxillary nerve from the middle cranial fossa; the pterygoid canal, the nerve and artery of the same name from the lower part of the anterior wall of the foramen lacerum ; and the palatinovaginal (pharyngeal) canal, which is frequently double, the pharyngeal nerve and artery to the roof of the posterior nasal aperture. The fourth foramen is placed on the medial wall and is termed the sphenopalatine foramen (fig. 332). It is bounded above by the body of the sphenoid, in front by the orbital process, behind by the sphenoidal process and below by the upper border of the perpendicular plate of the palatine bone. It transmits the long and short sphenopalatine nerves (nasopalatine and posterior superior lateral nasal nerves) and the artery of the same name. The fifth foramen is placed inferiorly at the junction of the anterior and posterior walls, and leads into the greater palatine canal (pterygopalatine canal). Bounded in front by the maxilla; and behind by the perpendicular plate of the palatine bone, this canal transmits the greater and lesser palatine nerves and vessels, which appear at the greater and lesser palatine foramina on the bony palate.
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