1) The pterion is located 35 mm behind and 12 mm above the frontozygomatic suture, estimated to be 2 fingerbreadths above the zygomatic arch. 2) The central sulcus can be approximated by connecting a point 2 cm posterior to the midline nasion-inion line to a point 5 cm straight up from the external acoustic meatus. 3) The lateral ventricles can be circumscribed by a quadrilateral with an upper limit 5 cm above the zygomatic arch, a lower limit 1 cm above the arch, and vertical limits through the zygomatic arch and 5 cm behind the mastoid process.

1. Surface anatomy of Brain
Dr Sameep Koshti

2. Auricular Point
The center of the orifice of the external acoustic meatus.
Preauricular Point
point on the posterior root of the zygomatic arch immediately in front of the external acoustic meatus.
Asterion
The point of meeting of the lambdoidal, mastoöccipital, and mastoparietal sutures;
it lies 4 cm. behind and 12 mm. above the level of the auricular point.
Pterion
The point where the the following bones are approximated:
frontal, parietal,temporal and sphenoid (greater wing).
it is situated 35 mm. behind, and 12 mm. above, the level of the frontozygomatic suture.
Estimated as 2 fingerbreadths above the zygomatic arch, and a thumb's breadth behind the frontal process of
the zygomatic Bone

3. Inion
The external occipital protuberance.
Lambda
The point of meeting of the lambdoidal and sagittal sutures;
it is in the middle line about 6.5 cm. above the inion.
Bregma
The meeting-point of the coronal and sagittal sutures;
it lies at the point of intersection of the middle line of the scalp with a line drawn vertically upward
through the preauricular point
• Stephanion
• junction of coronal suture and superior temporal line
• Glabella:
• the most forward projecting point of the forehead at the level of the supraorbital ridge in the midline.
• Opisthion:
• the posterior margin of the foramen magnum in the midline,

4. • The lambdoidal suture
• can be indicated on either side by the upper two-thirds of a line
• from the lambda to the tip of the mastoid process.
• The sagittal suture
• line joining the lambda to the bregma.
• Although often assumed to overlie the superior sagittal sinus
• the SSS lies to the right of the sagittal suture in the majority of specimens7 (but never by > 11 mm).
• The position of the coronal suture
• on either side is sufficiently represented by a line joining the bregma to the center of the
zygomtic arch.

5. 6. Reid’s base line:
line from inferior margin of orbit through the
centre of the external auditory meatus.

6. • Multiple methods, the most common being that developed by Taylor and Haughton.
• Recent analysis : accurate to within a few milimetres
• The lateral sulcus :
• sits on the frontozygomatic (Sylvian) line,
1. which passes from the frontozygomatic suture to a point 75% the way along the nasion–inion midsagittal
line.
2. The lateral sulcus extends postero-inferiorly from the
• Sylvian point : 1st method
• which practically corresponds to the pterion,
• is defined 35 mm. behind and 12 mm. above the level of the frontozygomatic suture;
• this point marks the spot where the lateral fissure divides., which is located around the region of the
pterion.
3. The lateral sulcus has also been shown to align with the anterior part of the squamosal suture in a zone
2.5–4.0 cm anterior to the external acoustic meatus
4. Another method of defining the Sylvian point and Sylvian fissure
• Intersection between following two points
• ¾ th of Nasion-inion midsagittal line to the frontozygomatic suture;
• ¼ th of Nasion-inion midsagittal line to the auricular point.
• The portion of the first line behind this point overlies the posterior ramus of the lateral cerebral
fissure.

7. • The central sulcus
• line passing
• from the superior Rolandic point : situated approximately 2 cm posterior to the midpoint of the nasion–inion midsagittal line,
• to the inferior Rolandic point: situated at the intersection of the frontozygomatic line with the pre-auricular/condylar line.
• Alternatively By Rhoton
• line passing from
• the superior Rolandic point to
• the midpoint of the zygomatic arch, with the central sulcus ending at the point of intersection of this line with the frontozygomatic line (Rhoton
2002).
• The precetral and postcentral sulci :
• are practically parallel to the central sulcus;
• they are situated respectively about 15 mm in front of, and behind, it.
• Parieto-occipital sulcus
• The superior extent:
• at the point of intersection of
• the frontozygomatic line and
• the 75% point on the nasion–inion line.
• OR
• from a point 5 mm. in front of the lambda
• To the inferior extent
• runs lateralward at right angles to the longitudinal fissure for about 2.5 cm.
• OR
• If the line of the posterior ramus of the lateral cerebral fissure be continued back to the longitudinal fissure, the last 2.5 cm. of it
will indicate the position of the parietoöccipital fissure.

8. • Motor cortex surface marking:
• These are just approximations
• since individual variability causes the motor strip to lie anywhere from 4 to 5.4 cm behind
the coronal suture.
• The central sulcus cannot even be reliably identified visually at surgery.
• method 1: the superior aspect of the motor cortex is almost straight up from the EAM
near the midline
• method 2: the central sulcus is approximated by connecting:
• A. the point 2 cm posterior to the midposition of Nasion-inion midsaggital line
• B. the point 5 cm straight up from the EAM
• method 3: using T-H lines, the central sulcus is approximated by connecting:
• A. the point where the "posterior ear line" intersects the circumference of the skull (usually about 1 em
behind the vertex, and 3-4 em behind the coronal suture), to
• B. the point where the "condylar line" intersects the line representing the sylvian fissure.
• method 4: a line drawn 45° to Reid's base line starting at the pterion points in the direction
of the motor strip

9. • The cerebellum
• no reliable surface marking for it;
• a point 4 cm. behind and 1.5 cm. below the level of the auricular point is situated directly
over it.

13. • Transverse sinus
• two lines:
• the first from the inion to a point 2.5
cm. behind the auricular point;
• the second from the anterior end of
the first to the tip of the mastoid
process. (Downgoing)
• upper two-thirds of second line
represents the sigmoid part of the
sinus.
• The first part of the sinus
• has a slight upward convexity, and
• its highest point is about 4 cm. behind
and 1 cm. above the level of the
auricular point.
• The width of the sinus is about 1 cm.

14. LATERAL VENTRICLES
• The lateral ventricle may be circumscribed by a quadrilateral figure.
• The upper limit is a horizontal line 5 cm. above the zygomatic arch;
• this defines the roof of the ventricle.
• The lower limit is a horizontal line 1 cm. above the zygomatic arch;
• the end of the inferior horn.
• Two vertical lines,
• one through the junction of the anterior and middle thirds of the zygomatic arch, and
• the other 5 cm. behind the tip of the mastoid process,
• indicate the extent of the anterior horn in front and the posterior horn behind these vertical line