Reference > Anatomy of the Human Body > Page 1294
Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.
border of the mastoid process at its root. A line from the upper end of the posterior line to the point where the anterior intersects the line of the posterior ramus of the lateral fissure indicates the position of the central sulcus. 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. The superior frontal sulcus can be mapped out by a line drawn from the junction of the upper and middle thirds of the precentral sulcus, in a direction parallel with the longitudinal sulcus, to a point midway between the middle line of the forehead and the temporal line, 4 cm. above the supraorbital notch. The inferior frontal sulcus begins at the junction of the middle and lower thirds of the precentral sulcus, and follows the course of the superior temporal line.

FIG. 1198– Relations of the brain and middle meningeal artery to the surface of the skull. 1. Nasion. 2. Inion. 3. Lambda. 4. Lateral cerebral fissure. 5. Central sulcus. AA. Reid’s base line. B. Point for trephining the anterior branch of the middle meningeal artery. C. Suprameatal triangle. D. Sigmoid bend of the transverse sinus. E. Point for trephining over the straight portion of the transverse sinus, exposing dura mater of both cerebrum and cerebellum. Outline of cerebral hemisphere indicated in blue; course of middle meningeal artery in red. (See enlarged image)

  The horizontal limb of the intraparietal sulcus begins from the junction of the lower with the middle third of the postcentral sulcus and curves backward parallel to the longitudinal fissure, midway between it and the parietal eminence; it then curves downward to end midway between the lambda and the parietal eminence. The external part of the parietoöccipital fissure runs lateralward at right angles to the longitudinal fissure for about 2.5 cm. from a point 5 mm. in front of the lambda. 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.
  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; it indicates the level of 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.

Vessels.—The line of the anterior division of the middle meningeal artery is equidistant from the frontozygomatic suture and the zygomatic arch; it is obtained by joining up the following points: (1) 2.5 cm., (2) 4 cm., and (3) 5 cm. from these two landmarks. The posterior division can be reached 2.5 cm. above the auricular point.
  The position of the transverse sinus is obtained by taking 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. The second line corresponds roughly to the line of reflection of the skin of the auricula behind, and its upper two-thirds 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.

The Face.—Air Sinuses (Fig. 1199).—The frontal and maxillary sinuses vary so greatly in form and size that their surface markings must be regarded as only roughly approximate. To mark out the position of the frontal sinus three points are taken: (1) the nasion, (2) a point in the middle line 3 cm. above the nasion, (3) a point at the junction of the lateral and intermediate thirds of the supraorbital margin. By joining these a triangular field is described which overlies the greater part of the sinus. The outline of the maxillary sinus is irregularly quadrilateral and is obtained by joining up the following points: (1) the lacrimal tubercle, (2) a point on the zygomatic bone at the level of the inferior and lateral margins of the orbit, (3) and (4) points on the alveolar process above the last molar and the second premolar teeth respectively.

External Maxillary Artery.—The course of this artery on the face may be indicated by a line starting from the lower border of the mandible at the anterior margin of the Masseter, and running at first forward and upward to a point 1 cm. lateral


Check out our other writing samples, like our resources on Skin Cancer Essay, Shopping Essay, Shakespeare Richard III Essay.

Shakespeare · Bible · Strunk · Anatomy · Nonfiction · Quotations · Reference · Fiction · Poetry
© 1993–2015 · [Top 150] · Subjects · Titles · Authors · World Lit.