HUMAN ANATOMY – VOLUME 1

Fig. 53. External surface of cranium base.

1 — palatine process of maxilla; 2 — incisive foramen; 3 — median palatine suture; 4 — transverse palatine suture; 5 — choane; 6 — inferior orbital fissure; 7 — zygomatic arch; 8 — vomer wing; 9 — pterygoid fossa; 10 — lateral plate of pterygoid process; 11 — pterygoid process; 12 — oval opening; 13 — mandibular fossa; 14 — styloid process; 15 — external acoustic opening; 16 — mastoid process; 17 — mastoid notch; 18 — occipital condyle; 19 — condylar fossa; 20 — foramen magnum; 21 — inferior nuchal line; 22 — external occipital protuberance; 23 — pharyngeal tubercle; 24 — condylar canal; 25 — jugular opening; 26 — occipitomastoid suture; 27 — external carotid opening; 28 — stylomastoid opening; 29 — foramen lacerum; 30 — petrotympanic fissure; 31 — spinous foramen; 32 — articular tubercle; 33 — sphenoidosquamous suture; 34 — pteryogoid hamulus;

35 — greater palatine opening; 36 — zygomaticomaxillar suture.

the sphenoid bone in the back, and by the perpendicular plate of the palatine bone on the medial side. The pterygopalatine fossa has no lateral wall and connects on this side with the infratemporal fossa. Five foramina open into the pterygopalatine fossa. On the medial side it communicates with the nasal cavity through the sphenopalatine foramen and with the middle cranial fossa through the foramen rotundum. In the back the pterygopalatine fossa communicates with the region of the lacerated foramen through the pterygoid canal, with the orbit through the inferior orbital fissure and with the oral cavity though the greater palatine canal. These and several other foramina serve as passages for blood vessels, cranial nerves and their branches.

The external base of the skull (básis cránii extérna) can not be seen from the front, because it is covered by the facial skull (Fig. 53, table 1).

It can be seen, however, that in the back it is formed by external surfaces of the temporal, sphenoid and occipital bones. The center of this region is the foramen magnum. Occipital condyles and condylar fossae are situated on the inferior surface of the external base. The base of each condyle is pierced through by a hypoglossal canal of the homonymous nerve. On either side of the occipital bone is an inferior surface of the pyramid of the temporal bone, on which one can see the external opening of the carotid canal, the musculotubal canal, the jugular fossa and the jugular notch. This notch forms the j u g u l a r f o r a m e n together with the jugular notch of the occipital bone. Also on the inferior surface of the pyramid are the styloid process, the mastoid process and the stylomastoid foramen, though which the facial nerve exits the skull. Lateral to the pyramid is the tympanic part of the temporal bone, which surrounds the external acoustic opening. In the back the tympanic part is connected with the mastoid process by the tympanomastoid fissure. The foramen ovale and foramen spinosum can be seen on the back part of the greater wing of the sphenoid bone, which lies between the petrous and squamous parts of the temporal bone. The pyramid and the greater wing of the sphenoid bone are separated by the petro-occipital fissure. There is also a f o r a - m e n l a c e r u m, which is limited laterally and from behind by the apex of the pyramid and the greater wing of the sphenoid bone.

The internal base of the skull (básis cránii intérna) has a concave surface. It is divided into the anterior, posterior and middle cranial fossae, in the bottoms of which there are various foramina (Fig. 54, table 2).

The a n t e r i o r c r a n i a l f o s s a (fóssa cránii antérior) is formed by the orbital parts of the frontal bone. The boundary between the anterior and middle fossae is the posterior edge of the lesser wings of the sphenoid bone. The cribriform plate of the ethmoid bone is situated in the central

Fig. 54. Internal surface of cranium base.

1 — orbital part of frontal bone; 2 — crista galli; 3 — cribriform plate; 4 — optic canal; 5 — hypophisial fossa; 6 — dorsum sellae; 7 — foramen rotundum; 8 — foramen ovale; 9 — foramen lacerum; 10

— foramen spinosum; 11 — internal acoustic opening; 12 — jugular foramen; 13 — hypoglossal canal; 14 — lambdoid suture; 15 — clivus; 16 — groove for transverse sinus; 17 — internal occipital protuberance; 18 — foramen magnum; 19 — squamous part of occipital bone; 20 — groove for sigmoid sinus; 21 — pyramis; 22 — squamous part of temporal bone; 23 — greater wing of sphenoidal bone: 24 — lesser wing of sphenoidal bone.

part of the anterior cranial fossa. The m i d d l e c r a n i a l f o s s a (fóssa cránii média) is formed by the body and greater wings of the sphenoid bone. It is separated from the posterior cranial fossa by the superior margin of the pyramid of the temporal bone and the dorsum of sella turcica.

The sella turcica is situated in the center of the middle cranial fossa. At its bottom is the pituitary fossa, in front of which is the prechiasmatic groove. On either side of this groove is an opening into the optic canal, which leads into the orbit. At each side of the sella turcica there is a carotid groove, formed by the adjoining carotid artery. Near the top of the pyramid of the temporal bone there is a lacerated foramen. Between the greater and lesser wings of the sphenoid bone is the superior orbital fissure, which connects the middle cranial fossa with the orbit. To the back of this fissure is the foramen rotundum, behind which is the foramen ovale. The foramen spinosum is situated laterally and to the back of the foramen ovale. In the posterior region of the middle cranial fossa, on the anterior surface of each pyramid there is a trigeminal impression of the large trigeminal ganglion of the homonymous nerve. Also on this surface are the hiatuses of the greater and the lesser petrosal nerves, grooves for the greater and lesser petrosal nerves and the arcuate prominence of the tegmen tympani. The p o s t e r i o r c r a n i a l f o s s a (fóssa cránii postérior) is formed by the occipital bone, posterior surfaces of the pyramids and part of the sphenoid bone body. In the back the posterior cranial fossa is limited by the groove of the transverse sinus. In the center of this fossa is the foramen magnum. In front of the foramen magnum there is a slightly sloping platform called the clivus, formed by fusion between bodies of the occipital and sphenoid bones. Behind the foramen magnum is the internal occipital crest. The posterior cranial fossa contains the internal auditory openings, which lead into the internal acoustic canals. The right and left jugular foramina and hypoglossal canals are also well seen.

Bones of the facial skull form parts of walls of the orbit, nasal and oral cavities and pterygopalatine and infratemporal fossae.

The o r b i t (o r b ít a) has the shape of a quadrilateral pyramid (Fig. 55). It contains the eyeball and the accessory apparatus of the eye, including muscles, the lacrimal glands, etc. The orbit has four walls, namely the superior, inferior, lateral and medial. The superior wall is formed by the orbital part of the frontal bone and the lesser wing of the sphenoid bone (from behind). The inferior wall consists of orbital surfaces of the maxilla and zygomatic bone and the orbital process of the palatine bone. The inferior wall has an infraorbital groove, which continues into the infraorbital canal in the front. The medial wall is formed by the frontal process of the maxilla, the lacrimal bone, the orbital plate of the ethmoid bone and the sphenoid bone body. The upper part of the medial wall is formed by the medial section of the orbital portion of the frontal bone.

The lower anterior part of the medial wall contains the n a s o l a c r i - m a l ca n a l (canális nasolacrimális), which opens into the inferior meatus of the nasal cavity. Above the o p e n i n g o f t h e n a s o l a c r i m a l

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c a n a l is the f o s s a o f t h e l a c r i m a l s a c. Behind and above this fossa, in the suture between the frontal bone and the orbital plate of the ethmoid bone are the a n t e r i o r and p o s t e - r i o r e t h m o i d f o - r a m i n a. The lateral wall is formed by the orbital surfaces of the greater wing of the sphenoid bone, the frontal process of the zygomatic bone and a small portion of the zygomatic process of the frontal bone. Between the lateral and the medial wall is

The i n f e r i o r o r - b i t a l f i s s u r e is also situated between the lateral and medial walls and connects the orbit with the pterygopalatine and infratemporal fossae. On the lateral orbital wall, in the area of the orbital surface of the zygomatic bone, is the zygomatico-orbital foramen. This foramen leads into a canal, which bifurcates and ends as the zygomaticofacial and zygomaticotemporal foramina on the lateral and temporal surfaces of the zygomatic bone accordingly.

T h e n a s a l c a v i t y (c a v u m n a s i) consists of a right and left halves, separated by the nasal septum. The b o n y n a s a l s e p t u m is formed by the perpendicular plate of the ethmoid bone, connected with the vomer. The front of the nasal cavity opens as the piriform aperture. The p i r i f o r m a p e r t u r e is formed by the nasal notches of the maxillae and the lower borders of the nasal bones. The posterior openings of the nasal cavity, which are called c h o a n a e (choánae), lead into the nasatpharynx. The choanae are limited by the medial plates of pterygoid processes on the lateral sides, the vomer on the medial side, the body of the sphenoid bone at the top and the horizontal plates of the palatine bones on the bottom.

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The nasal cavity has superior, inferior and lateral walls. The superior wall is formed by the nasal bones, the nasal part of the frontal bone, the cribriform plate of the ethmoid bone and the inferior surface of the sphenoid bone. The inferior wall of the nasal cavity is formed by the palatine processes of the maxillae, connected with the horizontal plates of the palatine bones. The lateral wall has the most complex structure (Fig. 56).

It is formed by the frontal processes of the maxillae and the nasal surface of its body, the lacrimal bone, the ethmoidal labyrinths, the per-

Fig. 56. Lateral wall of nasal cavity.

1 — cribriform plate; 2 — superior nasal concha; 3 — medial nasal concha; 4 — uncinate process of ethmoidal bone; 5 — sphenoid sinus; 6 — sphenopalatin foramen; 7 — maxillary hiatus; 8 — medial plate of pterygoid process; 9 — horisontal plate of palatine bone; 10 — palatine process of maxilla; 11 — inferior nasal concha; 12 — incisive canal; 13 — anterior nasal spine; 14 — inferior nasal meatus; 15 — middle nasi meatus; 16 — frontal process of

maxilla; 17 — superior nasi meatus; 18 — nasal bone; 19 — frontal sinus.

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pendicular plates of the palatine bones and the medial plates of the pterygoid processes. There are three bony nasal conchae fixed on the lateral wall: the superior and middle nasal conchae (parts of the ethmoid bone) and the inferior nasal concha (an independent bone). Between the conchae there are three nasal meatuses: the superior, middle and inferior.

The s u p e r i o r n a s a l m e a t u s (m e á t u s n ás i s u p é r i o r) is situated in the back section of the nasal cavity. It is the shortest and is limited by the superior and middle nasal conchae. It communicates with posterior ethmoidal air cells and the sphenoid sinus.

The m i d d l e n a s a l m e a t u s (m e á t u s n á s i m é d i u s) is situated under the middle nasal concha. It is twice as large as the superior meatus and is limited by the middle and inferior nasal conchae. It is communicated with the anterior and middle ethmoidal air cells, the frontal and the maxillary (Highmore) sinuses. Behind the middle nasal concha is the sphenopalatine foramen, which connects the middle nasal meatus with the pterygopalatine fossa.

The i n f e r i o r n a s a l m e a t u s (m e á t u s n á s i i n f é r i o r) is formed between the inferior nasal concha and the bottom of the nasal cavity. It contains the opening of the nasolacrimal canal.

Paranasal sinuses

The maxillary (Highmore) sinuses are cavities inside the maxilla. The anterior wall of each sinus is very thin in the center and gets thicker at the periphery. This wall is formed by a part of the maxilla between the infraorbital border and the alveolar process. Its lateral posterior wall corresponds to the maxillary tuber. The nasolacrimal duct passes within the anterior section of the medial wall, and the ethmoidal air cells lie close to its upper posterior section. The inferior wall is formed by the alveolar process of the maxilla. The superior wall of each sinus simultaneously acts as the inferior wall of an orbit. The maxillary sinuses open into the middle nasal meatus. The shape and size of these sinuses varies between individuals.

The frontal sinuses (sínus frontális) are highly variable in size. The septum dividing the left and right frontal sinuses is frequently asymmetrical. The frontal sinuses are communicated with the middle nasal meatuses.

The sphenoidal sinus (sínus sphenoidális) is located inside the body of the sphenoid bone. Its inferior wall forms part of the wall of the nasal cavity. The upper part of the lateral walls lies adjoining the cavernous sinuses. The sphenoidal sinus is frequently divided into two asymmetrical

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parts by a sagittal septum, although sometimes this septum is absent. The sphenoidal sinus is connected with the superior nasal meatus.

The anterior, middle and posterior ethmoid air cells are communicated with the nasal cavity.

The bony (hard) palate (palátum ósseum) is the bone base of the upper wall of the oral cavity and the bottom of the nasal cavity. The hard palate is formed by the palatine processes of the right and left maxillae and horizontal plates of the palatine bones, joint along the middle line by the median palatine suture. The alveolar arch of the maxillae limits the hard palate at the front and sides. In the anterior section of the median suture there is a foramen called the in c i s i v e c a n a l. The posterior borders of palatine processes are joined with the horizontal plates of the palatine bone by the transverse palatine suture. Behind the lateral section of this suture, on each horizontal plate, there is an opening of the g r e a t e r p a l a t i n e c a n a l and two or three foramina of the l e s s e r p a l a t i n e c a n a l s. These foramina link the oral cavity with the pterygopalatine fossa (Fig. 57). These canals serve as passages for nerves and blood vessels.

Fig. 57. Pterygopalatine fossa, (zygomatic bone partially removed).

1 — sphenopalatine foramen; 2 — pterygoid canal; 3 — greater palatine canal; 4 — pterygopalatine fossa.

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Table 1. External foramina of the skull base.

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Table 2. Internal foramina of the skull base.

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