Part 3

The scalp moves freely over the pericranium, to which it is very loosely connected by areolar tissue. When suppuration takes place in this tissue free incisions through the dense scalp must be made to let the pus out.

4. =Arteries of scalp.=--The supra-orbital artery can be felt beating just above the supra-orbital notch, and traced for some way up the forehead; the temporal (anterior branch) ascends tortuously about one inch and a quarter behind the external angular process of the frontal bone; the occipital can be felt near the middle of a line drawn from the occipital protuberance to the mastoid process; the posterior auricular, near the apex of the mastoid process. All these arteries can be effectually compressed against the subjacent bone.

5. =Skull-cap.=--The skull-cap is rarely quite symmetrical. This want of symmetry is often obvious. It may occur in men highly gifted, as in the celebrated French anatomist Bichat. As to shape and relative dimensions, no two heads are exactly alike, any more than are two faces. It is beside my present purpose to go into the question of craniology more than to say that, although the cranium does not exactly follow the brain in all its eminences and depressions so as to be like a cast of its surface, yet it certainly indicates the dimensions of the great cerebral masses. The prominence of the frontal and parietal ‘eminences’ and of the occipital region may be taken as a general indication of the development of the corresponding lobes of the brain. To ascertain the relative proportions of these three regions, let a thread be passed from one meatus auditorius to the other, across the frontal, parietal and occipital eminences respectively.

=Frontal sinuses.=--The ‘frontal sinuses’ formed by the separation of the two tables of the skull vary much in size in different persons and at different periods of life. This fact has an important bearing on wounds in the forehead and on trephining in this situation. These ‘bumps’ do not exist in children, because the tables of the skull do not begin to separate before puberty. From an examination of many skulls in the Hunterian Museum, I find that the absence of the ‘bumps,’ even in middle age, does not necessarily imply the absence of the sinuses, since they may be formed by a retrocession of the inner wall of the skull. In old persons, as a rule, when the sinuses enlarge, it is by the encroachment of the inner table on the brain case. The inner wall of the skull here follows the shrinking brain. It is, therefore, important to bear in mind that an adult, and more especially an elderly person, may have a large frontal sinus without any external indication of it.

Neither does a very prominent bump necessarily imply the existence of a large sinus, or indeed of even a small one. The ‘bump’ may be a mere heaping up of bone, a degradation, as in some Australian skulls.

=Mastoid process.=--The mastoid process, which can be felt behind the ear, contains air-cells, to which the above observations may also be applied.

=Occipital protuberance.=--The occipital protuberance, and the superior curved line, can be distinctly felt at the back of the head. The protuberance is always the thickest part of the skull-cap, and more prominent in some than in others.

The posterior inferior angle of the parietal bone, grooved by the lateral sinus, is on a level with the zygoma, and a trifle more than one inch behind the front border of the mastoid process.

=Lines of cerebral sinuses.=--A line drawn over the head from the root of the nose to the occipital protuberance corresponds with the superior longitudinal sinus. Another line drawn from the occipital protuberance to the front border of the mastoid process corresponds with a part of the lateral sinus.

=Middle meningeal artery.=--The trunk of the middle meningeal artery runs along the front lower corner of the parietal bone, about one inch and a half behind, and half an inch above, the external angular process of the frontal.

A straight line drawn from the front of one mastoid process to the other would pass through the middle of the condyles of the occiput, showing how nearly the skull is balanced on the top of the spine in the erect posture.

6. =Thickness of skull-cap.=--The average thickness of the cap of an adult skull is about ⅕ of an inch. The thickest part is at the occipital protuberance, where it is often ¾ of an inch or more, even in an otherwise thin skull. The thinnest part is at the temple, where it may be almost as thin as parchment. Everyone in the habit of making post-mortem examinations knows how much the skull-cap differs in thickness in different persons and in different parts of the same skull. In old persons it is often in some parts not thicker than a shilling, owing to absorption of the diploë. Another point of interest is that the inner plane of the cap is not always parallel with the outer. Hence, in applying the trephine this is not a bad rule--‘Think that you are operating on the thinnest skull ever seen, and thinner in one half of the circle than the other.’

7. =Levels of the brain.=--The level of the anterior lobes in front corresponds with a straight line drawn across the forehead, just above the eyebrows. The lower level of the anterior and middle lobes of the cerebrum corresponds with a line drawn from the external angular process of the frontal bone to the upper part of the meatus auditorius. Another line drawn from the meatus to the occipital protuberance corresponds with the lower level of the posterior lobe. The lower level of the cerebellum cannot be defined by external examination. It depends upon the extent to which the occipital fossæ bulge into the nape of the neck; and this bulge varies in different skulls.

THE FACE.

8. The approaches to the organs of the senses, their ever-varying expression, their numerous muscles, and their rich profusion of vessels and nerves, give the face great anatomical importance, which has a most valuable bearing, not only on the practice of surgery, but on the physiognomy of health, and in the diagnosis of disease.

9. =Foramina for branches of fifth nerve.=--As a surgeon may be called upon to divide any one of the three chief branches of the fifth nerve upon the face, he looks with interest to the precise situations where they leave their bony foramina with their corresponding arteries. The supraorbital notch or foramen can be felt about the junction of the inner with the middle third of the supraorbital margin. From this point a perpendicular line drawn with a slight inclination outwards, so as to cross the interval between the two bicuspid teeth in both jaws, passes over the infraorbital and the mental foramina. The direction of these two lower foramina looks towards the angle of the nose.

10. =Pulley for superior oblique muscle.=--By pressing the thumb beneath the internal angular process of the frontal bone, the cartilaginous pulley for the tendon of the superior oblique muscle can be distinctly felt. We should be careful not to interfere with this pulley in any operation about the orbit.

11. =Lower jaw.=--The working of the condyle of the jaw vertically and from side to side can be distinctly felt in front of the ear. When the mouth is opened wide, the condyle advances out of the glenoid cavity on to the eminentia articularis, and returns into its socket when the mouth is shut. The muscle which causes this advance is the external pterygoid; and it gives the jaw a greater freedom of grinding motion.

The posterior margin of the ramus of the lower jaw corresponds with a line drawn from the condyle to the angle. In opening abscesses in the parotid region, the knife should not be introduced behind this line for fear of wounding the external carotid artery. Punctures to any depth may be safely made in front of it. They are often necessary where inflammation of the parotid gland ensues after eruptive fevers, and runs on to suppuration. The swelling, tension, and pain are most distressing. Owing to the fibrous framework of the gland, the matter is not circumscribed, but diffused. One puncture is not enough. Three or more may be requisite. The blade of the knife should be held horizontally, so as to be less likely to injure the branches of the facial nerve. We are not to be disappointed if no matter flows. The punctures give relief, and matter will probably exude the next day.

12. =Parotid duct.=--A line drawn from the bottom of the lobe of the ear to midway between the nose and the mouth gives the course of the parotid duct. Opposite the second upper molar, the duct opens by a papilla into the mouth. The branch of the facial nerve which supplies the buccinator runs with the duct.

13. =Temporal and facial arteries.=--The pulsation of the trunk of the temporal artery can be felt, between the root of the zygoma and the ear. This should be well known to and used by chloroformists. It is also a convenient pulse to feel in a sleeping patient. The facial artery can be distinctly felt as it passes over the body of the jaw at the anterior edge of the masseter; again near the corner of the mouth close to the mucous membrane: and, lastly, by the side of the ala nasi, up to the inner side of the tendo oculi. By holding the lips between the finger and thumb the coronary arteries are felt under the mucous membrane. The facial vein does not accompany the tortuous artery, but runs a straight course from the inner angle of the eye to the front border of the masseter, just behind the artery.

14. =Eyelids and eyes.=--The opening between the eyelids varies in size in different persons; hence more of the eyeball is seen in some than in others, and the eye appears larger. Although human eyes do vary a little in size, yet the actual difference is by no means so great as is generally supposed. The size of the fissure has much to do with the apparent size of the eye. Contrast the narrow fissure of the Chinese and Mongolian races, and the apparent smallness of their eyes with those of Europeans. As a rule the external angle of the lid is higher than the internal. When not exaggerated, it gives the face an arch and pleasing expression.

Evert the lids to see the Meibomian glands; observe their perpendicular arrangement, in the substance of the tarsal cartilages.

The free borders of the lids are not bevelled, as described by J. L. Petit and most anatomists, ‘so as to form with the globe of the closed eye a triangular canal for the flow of the tears.’ On the contrary, it is easily seen that the lid margins, when closed, come into accurate contact. Their plane is not exactly horizontal, but slightly inclined upwards.

Every time the eye is shut, the ball turns upwards and inwards, so that the cornea is completely covered by the upper lid. This may be well seen by raising the lid of a sleeping infant; also in cases of low fever when the lid is not completely closed. This up-turning of the eye obviously clears the cornea, and protects it from the light.

A careful examination of the motion of the lower lid in the act of shutting the eye proves that it is a double motion. The lid is not only slightly raised, but drawn inwards about ¹⁄₁₂ of an inch. This second movement sweeps any particles of dust as well as moisture towards the inner canthus.

15. =Puncta lachrymalia.=--The puncta lachrymalia are distinctly visible at the inner angles of the lids. The lower punctum is larger and a little more external than the upper, so that they are not exactly opposite. The direction, too, of the puncta deserves notice. Their open mouths look a little backwards, ready to imbibe the tears. When their proper bearing is lost, as in facial paralysis or by a cicatrix near the lid, the tears overflow the cheek. The length of the lachrymal canals is from three to four lines. The lower is a little shorter and wider than the upper. As each makes a little angle in its course, about a line from its orifice, the lid should be drawn outwards to straighten the canal when we introduce a probe.

16. =Lachrymal sac.=--To find the lachrymal sac, draw outwards the eyelids to tighten the tendo oculi, which crosses the sac a little above its middle. A knife introduced just below the tendon close to the edge of the orbit would enter the sac. The angular artery and vein would be on the inner side of the incision. A probe directed in a line with the inner edge of the orbit, i.e. downwards, outwards, and backwards, would pass down the nasal duct, and appear in the inferior meatus of the nose.