1

RELATION OF THE BONES APPEARING THERE TO ONE ANOTHER.

MAXILLO-OCCIPITAL PART of the MESIAL LINE

..........

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This line is formed by that part of the mesial line from between the two front incisors of the upper jaw to the spinous process of the occipital bone; or, rather, it is a straight line joining these two points, and lying over the course of the mesial line.

Bisect this line. The point of bisection generally indicates the centre of the anterior margin of the foramen magnum of the occipital bone.

Divide the anterior half of this line into seven equal parts.

From all the points thus made, draw lines at right angles to this line, and, to the horizontal plane, in which it lies, and intersecting the mesial line.

The extremities of these lines will fall upon the following parts :

1st, On the anterior, inferior point of the meeting of the superior maxillary bones, immediately between the anterior alveolar processes of the front incisors of those bones.

2nd, On the centre of the posterior margin of a foramen, called incisivum 3rd, On the centre of the palate, or, half way between the foramen incisivum, and the anterior margin of the palatine bones.

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.....

30

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4th, On the point where the palatine suture of the superior maxillary bones meets the palatine suture of the palate bones.

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5th, On the point, where the palatine suture of the palate bones terminates posteriorly, that is, where the posterior curved edges of the palatine plates of the palate bone meet, and where the origins of the azygos uvula meet.

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6th, On the point immediately between the superior posterior termination of the vome,

and the central point of the junction of the anterior surface of the cunieform process of the occipital bone with the posterior surface of the body of the sphenoidal bone.

7th, On a little prominence on the centre of the cunieform process of the occipital bone, and the point where the anterior margins of the recti antici majores muscles

meet.

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8th, On the centre of the anterior margin of the foramen magnum of the occipital bone. The relations indicated above, by the aid of the divisions of the anterior half of the maxillo occipital part of the mesial line, hold in the different races of mankind, the chief deviation being an occasional unusual prolongation backwards of the points of the palatine plates of the palate bones.

The portion of the mesial line between 1 to 4 runs along the palatine suture of the superior maxillary bones; that from 4 to 5 runs along the longitudinal palatine suture of the palate bones.

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By the maxillo-occipital line, and its division into equal parts, we become acquainted with the relative position of the parts of the anterior of the base of the cranium lying along the mesial line. By drawing lines transverse, or at right angles to this line in the plane, on which the head is supposed to stand when deprived of the under maxillary bone, and continuing them to the bounding outline of the base of the cranium, we shall be able, by dividing these lines also into equal parts, to demonstrate what lies upon either side of the mesial line.

LINES TRANSVERSE to the MAXILLO OCCIPITAL LINE.

We make the first of these lines pass through the second point of the maxillo-occipital line. All of them are bounded by the outline, which the base of the cranium assumes, when we are looking vertically down upon it, the cranium being placed on its crown. From the points, obtained by division and termination of these transverse lines, straight lines must be allowed to drop vertically on to the nearest points of the base, which will by their terminations indicate the points we wish to name. As these lines will be the same on either side of the maxillo-occipital line; we need only name the points, on which they fall on one. side, and we shall consider the point, to which the maxillo-occipital line corresponds as No. 1, proceeding outwards with the numbers.

The 1st of the transverse lines passes behind the two single pointed teeth called canine, and before two double-pointed teeth called the anterior bicuspids. Divide it into two equal parts; It may be called

Canino-bicus

pidal line

1, Falls on

2,

3,

THE CANINO-BICUSPIDAL LINE

}

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the centre of the posterior margin of the foramen, called incisivum. of a band, or ridge of bone, separating the canine from

{the bicuspid, and called the transverse alveolar process.

the point in the lower part of the margin of the socket of the
eye, at which the malar bone, after overlapping the maxillary
bone, terminates.

2nd, Passes behind the two posterior teeth with two points, called the posterior bicuspids, and before two teeth with five points called the anterior molares. Divide it into two equal parts; It may be called

Bicuspido-molar line

1, Falls on

2,

3,

THE BICUSPIDO-MOLAR LINE

the centre of the bony table between the teeth, called the
Palate, that is, half way between the posterior margin of the
foramen incisivum, and the anterior mesial point of the palate
bones.

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39

40

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the centre of the band or ridge of bone between the bicuspid and molares, called the transverse alveolar process.

the centre of that part of the malar bone in the margin of the socket of the eye, where that bone begins to turn backwards.

3rd, Passes behind the two teeth having five points, and before two teeth having four points, which are called posterior Molares. Divide it into two equal parts; It may be called

the centre of the anterior termination of the palate bones. Sthe centre of the band or wedge of bone between the anterior and posterior molars, called the transverse alveolar process. the centre of the lower part of the suture joining anteriorly the maxillary and malar bones, that is, on the anterior point of the insertion of a muscle called Masseter.

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4th, Passes between the posterior inferior part of the maxillary, and the posterior lateral part of the palate bones. Divide it into three equal parts; It may be called

THE MAXILLO-PALATINE LINE

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the centre of the posterior edge of the plates of the palate bones
forming part of the palate, that is, just in the point, where the ori-
gins of the muscles called azygos uvulæ meet.

the central point between the posterior inferior lateral pro-
duction of the palate bones, called their pterygoid process, and
the posterior termination of those processes of the superior
maxillary, called alveolar processes.

the centre of the posterior part of a ridge running inwards and
forwards to the mesial line upon the sphoenoid bone, dividing
the great lateral production of the sphenoid, called its greater
wing, into two nearly equal parts, one of which faces towards
the side of cranium, and is called the temporal plate of the
sphoenoid, the other towards its base: at this point the ridge is
crossed by a suture, called the sphæno-temporal.
́the centre of an arch of bone called the zygoma, where that
arch is formed by the junction of a production from the malar
and from the temporal bone, that is, in the centre of a suture
called zygomatic, that is, in the centre of the termination,
posteriorly, of the origin of a muscle called Masseter.

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5th, Passes along the line of junction of the cunieform process of the occipital bone with the posterior surface of the sphoenoid. Divide it into three equal parts; It may be called

Sphoeno-occipital line

1, Falls on

3,

4,

THE SPHENO-OCCIPITAL LINE

the centre of the line of junction of the occipital and sphoenoid.
the anterior point of the long diameter of a foramen, called
ovale. The long diameter of this foramen inclines outwards and
backwards from the mesial line from this point. The vertical
line, whose lower point indicates this foramen, drops in its
course downwards from the plane, 1st, on the point of junction
between the inferior exterior termination of the transverse pro-
cess of the palate bone called pterygoid, and the lower anterior
edge of a plate of the sphenoid diverging along the long dia-
meter of the foramen ovale from the mesial line, called the ex-
ternal pterygoid process of the sphenoid. The vertical line,
proceeding downwards, nearly bisects this plate, and, finally,
terminates at the posterior part of the root of the same, which
indicates the anterior point of the long diameter of the foramen
ovale.

the suture at the base of the cranium, called sphæno-temporal.
the centre of the flat origin of the process of the temporal,
which goes to form the lateral arch or zygoma, and therefore
called zygomatic.

6th, Passes across the cunieform process of the occipital bone. Divide it into three equal parts: It may be called

THE CUNIEFORMI-OCCIPITAL LINE

the centre of the mesial line of the cunieform process of the
occipital bone, on a little prominence which lies between the
anterior margins of two muscles, called recti antici majores.
the slit between the side of the cunieform process of the
occipital bone, and the interior edge of the scabrous part
of the temporal, called pars petrosa.

the junction between the prominent posterior lateral termi-
nation of the sphenoidal, called its spinous process, and a cor-
responding prominence of the pars petrosa of the temporal bone,
immediately above an orifice, called iter a palato ad aurem.
the centre of a little prominence immediately anterior to a
furrow proceeding outwards from the last mentioned point,
and called fissura condyloidea.

7th, Passes along the anterior points of those parts of the occipital, which being in apposition with the first bones of the spine, are called condyles. Divide it into three equal parts; it may be called

1, Falls on

THE CONDYLOIDEO-OCCIPITAL LINE

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the centre of the anterior margin of the foramen magnum of the occipital bone.

Condyloideo-occipital line

2,

the exterior anterior superior margin of the anterior condyloid
foramen, that is, on a septum or band of bone dividing
this foramen from a large irregular hole or cavity which is
called fossa jugularis. This line from 2 to 3 crosses the longest
diameter of this fossa jugularis.

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3,

the anterior interior part of the root of a very long process
called Styloid.

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the centre of the superior part of a ridge bounding a large
orifice, called meatus auditorius externus.

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4,

Immediately behind No. 4 of the last mentioned line there is a very large irregular projection from the temporal bone called the Mastoid, or mamillary, process. If we make a line to join the anterior points of the roots of these processes, we shall have another line transverse to the mesial line. Divide the half of this line, as in the former cases, into four equal parts; it may be called

THE MASTOIDEO-OCCIPITAL LINE.

the mesial line of the foramen magnum of the occipital bone,
at a point distant about a quarter of the length of the foramen
from No. 1 of the condyloideo-occipital line, the point, through
which any lever, passed through this foramen, and support-
ing the cranium in a state of equilibrium, passes.

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the inner margin of the condyloid process of the occipital bone, at a point distant about one-third from the anterior point of that process. The vertical line, if produced downwards, crosses the posterior edge of the interior margin of the foramen, called anterior condyloid for

amen.

the inner posterior condyloid margin of the fossa jugularis. This line between 3 and 4 skirts the posterior margin of the same fossa. the inner margin of a small foramen, situated without the exterior edge of the fossa jugularis, called foramen stylomastoideum.

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the point between the mastoid process, and the ridge surrounding the meatus auditorius externus.

These lines promise to be of the greatest utility in enabling us to indicate at once the situation of the parts in this complex region. For, in the first place, we may readily point out between which two of the lines any part lies, and, then, by giving the numbers in these lines, which are to be joined by imaginary straight lines, fix the boundaries, to which any part extends.

(See the Analytical Table of the Contents, on the opposite page.)

Which passes o'er the Ocean of the mind

Lest it should stagnate, and become the grave

Of gems committed to its living wave;

Think ye this natural world would bloom so fresh and fair,
If storms ne'er rose to purify the air?

Does not the thunder on its flery wing

Oftimes a glow of balmy freshness bring?

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