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TOPOGRAPHIC ANATOMY
OF THE CEREBRAL PART OF THE HEAD
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The head is divided into two parts: cerebral and facial. The border between them
is the line which is drown along the superior margin of the orbit and further along the
zygomatic arch to the apex of the mastoid process. From the latter the border goes along
superior nuchal line (Fig. 1).
Cerebral part includes the fornix and the base of the skull. The fornix of the skull
is divided into three regions: frontopaÂrietooccipital or scalp, temporal and the region of
the mastoid process.
The cranial cavity contains the brain and surrounding meninges, portions of the
cranial nerves, arteries, veins and veÂnous sinuses.
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Fig. 1. Landmarks of the skull.
The brain is well protected from the environment by the boÂnes of the fornix and
the base of the skull and also by the inner skeleton formed by the dura mater and
cerebrospinal fluid (CSF). Cerebrospinal fluid fills the ventricles and subarachnoid space.
The brain seems "to float" in the watery media, so being, semiliÂquid, just as
cerebrospinal fluid, it can't be compressed. It leÂads to the concussion and contusion of
the brain and other lesiÂons.
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FRONTOPARIETOOCCIPITAL REGION
The border passes from the superior margin of the orbit and further along the
superior temporal line, base of the mastoid process, superior nuchal line to the external
occipital protubeÂrance and passes on to another side.
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Fig. 2. Layers of a fornix of
the skull on frontal section
drawn through the
frontoparietooccipital region
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1 – skin, 2 – subcutaneous
tissue, 3 – aponeurosis, 4
– diploic vein, 5 –
subaponeurotic fat, 6 –
periosteum, 7 –
subperiosteal fat, 8 - arachnoid
granulations, 9 – epidural
hematoma due to injury of the
medial meningeal artery (10),
11 – dura mater, 12 –
arachnoid mater, 13 – CSF
of subarachnoid space, 14 –
pia mater, 15 – cortex, 16
– falx cerebri, 17 –
superior sagittal sinus, 18 –
veins of brain, 19 – vein and
artery of dura mater, 20 –
epidural space, 21 – internal
table of compact bone, 22 –
diploё, 23 – external table
of compact bone, 24 –
emissary vein, 25 –
subcutaneous vessels, 26 –
fibrous septa connecting skin
with aponeurosis
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The scalp is the covering of the cranial vault. It consists of five layers, but the first
three of which are bound together and move as a unit.
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The skin (1) of the scalp is normally covered by coarse hairs. Skin is thick and
dense and contains many sebaceous glands.
BeneÂath the skin there lies subcutaneous tissue (2). It consist of a denÂse
network of fibrous tissue containing only small lobules of fat. The fibrous septa connect
the skin with underlying aponeuroÂsis of the occipitofrontalis muscle. Within
subcutaneous tissue there lie the vessels and nerves. The arteries are branches
of the external and a free anastomosis takes place between them. AdÂventitia of the
vessels is connected with fibrous septa and so the lesion of them results in massive
hemorrhage, as they don't contract, but gape.
Pressing with finger tips on the borders of the wound or applying a pressing
dressing is the first aid to stop arrest hemorrhage in such lesion.
The muscular layer (3) consists of the frontalis muscle anteriÂorly and the
occipitalis muscle posteriorly. The two muscles are united by a broad aponeurosis, the
galea aponeurotica or epicraÂnial aponeurosis. Each occipital belly arises from the
highest nuchal line on the occipital bone and passes forward to by attaÂched to the
aponeurosis. It is supplied by the posterior branch of the facial nerve. Each frontal belly
arises from the skin and superficial fascia of the eyebrow and passes backward to be
atÂtached to the aponeurosis. It is supplied by the temporal branch of the facial nerve.
The lateral margins of the aponeurosis are attached to the temporal fascia.
The subaponeurotic space (4) is the potential space beneath the epicranial
aponeurosis. This space is limited by the origins of the frontal and occipital muscles and
on each side by the attachÂment of the galea to the temporal fascia. Loose areolar tissue
occupies the subaponeurotic space. The areolar tissue contains a few small arteries, but
it also contains some important emissary veins. The emissary veins are valveless and
connect the superfiÂcial veins of the scalp with the diploic veins of the skull bones and
with the intracranial venous sinuses. Bleeding into this space often becomes manifested
as a bilateral black eye. The loose areÂolar layer between the scalp and the pericranium
is of clinical importance. Once an infection has reached the loose layer, it can spread
readily in it. Therefore, this layer has been called the "dangerous area". From the
"dangerous area" the infection is easily carried along veins that traverse the bony fornix
vault. As a result, the infection may spread to the substance of the bones, to venous
channels within the cranial cavity or to the brain.
Pericranium (5) is the periosteum on the external surface of the skull. It is attached
to the skull at the sutures, but it is eaÂsily stripped off the bone as beneath periosteum a
layer of subperiosteal fat (6) is located. It is the so called subperiosteal loose areolar
tisÂsue. Subperiosteal blood or pus is limited to one bone due to atÂtachment of the
periosteum to the sutures.
Sensory Nerve Supply of the scalp.
The anterior part of the scalp is supplied by the supratÂrochlear and supraorbital
nerves. The supratrochlear nerve is branch of the ophthalmic division of the trigeminal
nerve. The supraorbital nerve is also branch of the ophthalmic division of the trigeminal
nerve.
The temporal region is supplied by zygomaÂticotemporal nerve and
auriculotemporal nerve. The zygomaticotemÂporal nerve is a branch of the maxillary
division of the trigemiÂnal nerve. The auriculotemporal nerve is a branch of the
mandibuÂlar division of the trigeminal nerve.
The skin of the posterior part of the scalp is supplied by cervical spinal nerves. The
lesÂser occipital nerve is branch of the second cervical nerve and supplies the region
behind of the second cervical nerve.
The blood supply of the scalp.
The forehead and anterior part of the scalp are supplied by the supraorbital and
supratrochlear arteries, both branches of the ophthalmic artery, which is itself a branch of
the internal carotid artery.
The posterior part of the scalp is supplied by two further branches of the external
carotid artery. These are the posterior auricular and occipital arteries.
The parietal part of the region is supplied by the superficial temporal artery which
is a temporal branch of the external carotid artery.
These vessels supplying the scalp and the face communicate freely with each
other across the midline and are thus able to establish an effective collateral circulation
following obstruction or ligatiÂon of one external carotid artery. Blood from scalp is
drained by veins accompanying the arteries.
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Bones of the skull cup
The bones of the skull cap consist of two compact bones separated by an irregular
layer of cancellous bone. The compact bone forms the inner and outer tabÂles of the skull
and the cancellous bone which contains red bone marrow is called the diploё. The
diploÑ‘ contains the diploic veÂins which are connected with superficial veins of the scalp
and with the intracranial venous sinuses by means of emissary veins. A small foramen is
commonly present, which perforates each parieÂtal bone at the side of the sagittal
groove; it transmits an emissary vein from the superior sagittal sinus.
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THE TEMPORAL REGION
The superior temporal line, the frontal process of the zygomatic boÂne and the
zygomatic arch form the boundaries of the temporal (region) fossa. The layers of this
region are:
1) Skin.
2) Subcutaneous fat. Within subcutaneous tissue there lie the vessels and
nerves. These are the superficial temporal artery and the auriculotemporal nerve. The
auriculotemporal nerve emerges from the upper border of the parotid gland behind the
temporomandiÂbular joint and crosses root of the zygomatic arch behind the suÂperficial
temporal artery and in front of the auricle. The superÂficial temporal artery emerges from
the upper border of the paroÂtid gland behind the temporomandibular joint and crosses
the root of the zygomatic arch in front of the auriculotemporal nerve and the auricle. It is
here that its pulsation may be easily felt.
3) The next layer is superficial fascia.
Beneath the superficial fascia there lies the temporal fascia. It is attached to the
superior temporal line and below to the upper border of the zygomatic arch. The temporal
fascia is called the temporal aponeurosis. It consists of two sheets: suÂperficial (4) and
deep (6). The layer of fat is located between these sheets. It is called interaponeurotic
fat (5). This layer of fat is a closed fat space.
7) Beneath the deep sheet of temporal fascia (aponeurosis) the subaponeurotic
space is situated. Loose areolar tissue occuÂpies the subaponeurotic space. This areolar
tissue extends downÂward into the infratemporal fossa and then into the buccal fatpad
on the buccinator.
8) Beneath this areolar tissue the temporal fossa is occupied by the temporalis
muscle. The muscle arises from the bony floor of the temporal fossa and from the deep
surface of the temporal fascia. Tendon of the muscle passes deep to the zygomatic arch
and is attached to the borders of the coronoid process of the mandible and the anterior
borders of the ramus.
The deep temporal nerves are two in number and arise from the anterior division
of the mandibular nerve. They enter the deep surface of the temporaÂlis muscle. The
deep temporal arteries, also two in number, are branch of the maxillay artery. They
accompany the nerves and supply the temporalis muscle.
9) Beneath the temporal muscle periosteum is situated, which is attached to
bones of the temporal fossa (10). The floor of the fosÂsa can be seen to be formed by
the parietal, temporal, frontal and sphenoid bones.
The middle meningeal artery is located on inÂner surface of the bones of the
temporal fossa. The artery diviÂdes into anterior and posterior branches.
The anterior branch passed forward and upward to the anterior inferior angle of
the parietal bone. Here, the bone is deeply grooved or tunneled by the artery for a sport
distance before it runs backward and upward on the parietal bone. It is at this site that the
artery may be damaged following a blow to the side of the head.
The posterior branch passes backward and upward across the squamous part of
the temporal bone to reach the parietal bone.
The middle meningeal artery has of great clinical importance. If it is torn in
a head injury blood will quickly accumulate between the bony skull and dura mater
(epidural hematoma). The expanding hematoma may exert fatal pressure on the brain
unless it is recognized and surgically treated. Surgeons must be aware of the course
of the middle meningeal artery and its projection on the surface of the cranium.
Fractures through the bones of the temporal fosse are likely to result in tearing of the
middle meningeal artery with the conÂsequence of epidural hematoma.
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The scheme of cranio-cerebral toÂpography of Kronlein
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Fig. 3. The scheme of
cranio-cerebral toÂpography
of Kronlein
1 – superior horizontal line,
2 – inferior horizontal line,
3 – anterior vertical line,
4 – middle vertical line,
5 – posterior vertical line,
6 – projection of lateral
sulcus, 7 – projection of
central sulcus
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Projection of the middle meningeal artery and its branches on the cranium is
determined by the scheme of cranio-cerebral toÂpography Kronlein. The scheme is built
by the following way (Fig. 3).
Inferior horizontal line is drown from the inferior margin of the orbit and further
along the zygomatic arch and superior margin of the external acoustic meatus.
Superior horizontal line is drown from the superior margin of the orbit and parallel
to the inferior horizontal line.
Three vertical lines are drown perpendicularly to horizontal lines.
Anterior vertical (perpendicuÂlar) line is drawn from the middle of the zygomatic
arch.
Middle line is drawn from the temporomandibular joint.
Posterior vertiÂcal line is drawn from the posterior point of the base of the mastoid
process.
This vertical lines are continued to the sagitÂtal line, which is drawn from the base
of the nose to the exterÂnal occipital protuberance.
The trunk of the middle meningeal artery is determined in the point of the
intersection of ...
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