X

On the Vomer in Man ancl the Mammalia , and on the

Sphenoidal Spongy Bones. By John Cleland, M.D.,

Demonstrator of Anatomy in the University of Edinburgh.

The remarks which I am about to make will be confined as
much as possible to matters of observation. I shall resist the
temptation to enter on the question of the constitution of the
vomerine segment of the skull, although it is one on which
the statements to be made have an important bearing ; I shall
content myself with exhibiting the relations of this bone in
different mammalia, and, founding upon these and on develop-
ment, shall show how the vomer in man corresponds in its
relations to those of other animals, and what is the nature of
the sphenoidal spongy bones.

Last autumn, while disarticulating the skull of a lamb, it
came prominently under my notice that the central plate of
the sphenoid bone adhered without marks of separation to the
presphenoid, while the lateral masses of the ethmoid and the
vomer formed one other single piece. On further examination
I found that in mammalian skulls the formation of one piece
by the vomer and lateral masses of the ethmoid was the gene-
ral rule, and their separation a rare exception. This is a cir-
cumstance so easily seen that one would think it could hardly
escape the notice of any one in the habit of disarticulating
mammalian skulls, yet I can find no description of it by
authorities on human and comparative anatomy. It is, how-
ever, as we shall see, the most important of all the connections
of the vomer, and throws some valuable light on human ana-
tomy. With respect to the other articulations of the vomer,
we shall see, that that with the central plate of the ethmoid is
by no means a primary one, and that the most constant of those
of its inferior margin is that with the intermaxillary bones.

2

Dr John Cleland on the

In the ruminantia it is a well-developed elongated bone.
Let us take that of the lamb as an example. It consists
principally of two laminm united inferiorly so as to form a
groove ; deepest posteriorly where the laminae are most de-
veloped, and shallowing away to a scooped extremity in front.
In this groove lies the cartilaginous septum of the nose, which
is continuous behind with the presphenoid bone. The pos-
terior extremity of the vomer is bifid and slightly dilated, as
it is in man, and in front of the dilatation the lines of mar-
gin begin to approach, and seem as if they would pass directly
forwards; but they are almost immediately lost as fissures in
two lateral expansions, which, springing from the vomerine
laminae, pass outwards to the outer and back part of the
ethmoid, and are continuous with the principal arches of the
framework of that bone. On the upper aspect there is a sharp
angle between the lamina; that lie against the cartilaginous
septum and their lateral expansions, and the former are pro-
longed in many animals beyond the angle. Where the eth-
moid is joined by the ethmo-vomerine lamina — for so we shall
call the expansion just described — it forms the upper part of
the nasal foramen of the palate bone, in human anatomy
called the spheno-palatine foramen. In the lamb there is not
much development of the vomer as a mesial plate below the
level of the groove. It articulates inferiorly by a rough
sutured edge with the superior maxillary bones, and in front
of that its scooped anterior extremity lies for about an eighth
of an inch or so on the groove formed by the mesial processes of
the intermaxillary bones — the universal method of articulation
of the mammalian vomer with the intermaxillary bones (fig. 1).

The vomer of the cat is proportionally less elongated than
that of the sheep, but like it has little development of the
mesial plate beneath the vomerine groove. It articulates by
a rough surface with the superior maxillary and palate bones,
but with the intermaxillary bones by an elongation forward
upon them of the laminae which bound the groove. These
laminae are connected towards their back part with the lateral
masses of the ethmoid, exactly as is the case in the sheep ;
and at the point where the vomer passes into the ethmoid, the
latter presents a minute orbital surface, which lies between

3

Vomer in Man and the Mammalia.

the two ascending processes of the palate bone, and completes
by a point in its inferior margin the almost perfect nasal
foramen of that hone. The sphenoid process of the palate-
hone lies between the ethmo-vomerine laminae and the ptery-
goid bone. The central plate of the ethmoid does not at all
touch the vomer in early life, but the cartilaginous septum of
the nose passes back beneath it to the presphenoid bone.

It may be mentioned at once that the nasal foramen of the
palate bone is completed by the ethmoid in all the animals
examined.

The relations of the vomer in the fox and the pig are the
same as in the cat. In the case of the hedgehog, as in the
sheep, it does not articulate with the palate bones. In the
horse also it does not articulate with the palate bones. But the
superior connections of the vomer in the horse are peculiar,
inasmuch as the inferior surface of the leaflets of the ethmoid,
instead of lying in contact, as is usual, with the ethmo-vomerine
lamina for a considerable extent, is completely floored in by
the upper part of the palate bone, which is expanded for that
purpose. Even in the horse, however, a slender lamina, im-
mediately in front of the palate bone, and in contact with its
nasal foramen, passes downwards and inwards on each side
from the framework of the ethmoidal turbinations to the mar-
gin of the vomer ; but the vomer and it are not anchylosed
until other sutures also have begun to be obliterated.

The vomer in the rodenlia is remarkable in having very
little tendency to come in contact with the superior maxilla-
ries. As far as I have observed, it is always continuous with
the lateral masses of the ethmoid.

In the skull of the rabbit there is only one great anterior-
palatine foramen ; for, although the mesial processes of the
intermaxillaries project well backwards, the palate plates of
the superior maxillaries do not come far enough forwards to
meet them. The vomer does not at all approach the superior
maxillaries ; its posterior margin terminates inferiorly in a
thickened angle, which articulates with the intermaxillaries in
such a manner as to make their inferior aspect continuous
with the posterior margin of the vomer. In front of this,
the laminae bounding its groove are prolonged on the upper

4 Dr John Cleland on the

surface of the intermaxillaries, as we have seen in other
animals (fig. 4).

In the porcupine and squirrel the vomer is not in contact
with the superior maxillary bones ; in the rat and the heaver
it is.

In the quadrumana the mesial process of the intermaxil-
laries is so slightly developed that the anterior extremity of
the vomer frequently falls short of it by a slight interval. In
monkeys the vomer and orbital plates of the ethmoid are con-
tinuous ; but in the skull of a young Chimpanzee in the Uni-
versity Museum, the arch of bone which unites them is sepa-
rated at one extremity from the ethmoid by a suture, and at
the other only touches the vomer. This piece of bone has all
the essential characters of the sphenoidal spongy bones of the
human subject.

The vomer and sphenoidal spongy hones in man. — Having
found the vomer and lateral masses of the ethmoid so univer-
sally connected, we naturally inquire how they are related in
man. They are not in contact. Their only connection is
that the expanded portion of the vomer which grasps the
rostrum lies beneath the sphenoidal spongy bones, and that
these articulate with the lateral masses of the ethmoid. Now,
seeing that the sphenoidal spongy bones are recognised as
ossifications distinct from the sphenoid, I think we have
already sufficient evidence to prove that they represent the
etlirao-vomerine laminae, by aid of what we have noticed in
the Chimpanzee’s skull ; for it is impossible to doubt either
that the distinct bone which lies between the orbital plates of
the ethmoid and the vomer in that skull corresponds to the
ethmo-vomerine lamina of other monkeys ; or, on the other
hand, that it corresponds to the sphenoidal spongy bone in
man. But the correspondence becomes much more distinct
when we study the early condition of the sphenoidal spongy
bones. The most interesting condition of these bones is when,
in the skulls of young children, they can be got completely
ossified and not yet destroyed by amalgamation with the
neighbouring bones. In this state the sphenoidal spongy
bone is somewhat of the shape of a hollow pyramid with the
apex directed backwards, its inner aspect parallel to its fellow,

Vomer in Man and the Mammalia.

5

and its cavity (the first form of the sphenoidal sinus) opening
at its base into the nasal cavity in front (fig. 2). This pyramid
is constructed by the union of at least three distinct pieces of
bone. Firstly, there is an orbital piece, forming a portion of
the wall of the orbit between the ethmoid and sphenoid, an
element, I believe, in the formation of the orbital wall not
hitherto observed. It articulates with the orbital process of
the palate bone, and, together with the inferior piece, com-
pletes the nasal foramen of the palate-bone, namely, the fora-
men called spheno-palatine, but which we have seen to be
invariably ethmo-palatine in other animals. The superior
piece bounds the sphenoidal sinus above and on the inside,
and ultimately becomes incorporated with the sphenoid bone.
The inferior piece is the largest of the three ; it forms the
floor of the sphenoidal sinus, and the under half of its opening
in front, and includes the greater part of what has hitherto
been recognised, and described under the various names,
sphenoidal spongy bone, sphenoidal cornu, and bone of Bertin.
Its inner margin is joined by the superior piece at an acute
angle, and is prolonged downwards and forwards so as to lie
edge to edge with the corresponding lamina of the vomer, im-
mediately in front of the thick dilated part of that bone.
Beneath and behind is the sphenoidal process of the palate-
bone, and behind that is the internal pterygoid process. In
man, therefore, as in other mammalia, we find three processes
in succession from behind forwards, viz., the pterygoid bone,
the sphenoidal process of the palate-bone, and an arch passing
from the ethmoid to the vomer, adapted to it edge to edge ;
and moreover, this arch completes the foramen which divides
the ascending part of the palate-bone. It in every respect,
therefore, corresponds with the ethmo-vomerine lamina. The
reason why the arch formed by the vomer and ethmoid is
broken up in the human subject into so many separate pieces
is to be sought in the characteristic peculiarities of the human
subject, particularly in the very slight development of the
organ of smell, and the rapid curvature of the cranio-facial
arch. But on this subject I hope to speak more fully on some
future opportunity. The inferior edges of the sphenoidal
spongy bones, which in childhood lie edge to edge with the

6

Dr J ohn Cleland on the

vomer, are in the adult state smoothed down to a mere ridge,
and considerably separated from the middle line by the ex-
pansion of the sphenoidal sinuses.

We have nowseen that the relations of the vomer to the lateral
masses of the ethmoid in the human subject are essentially the
same as in the mammalia generally. In early life the human
vomer resembles those of other mammals in form likewise, and
seems to be connected in the same manner with the intermaxil-
lary bones. In the skulls of foetuses and young children the
vomer mainly consists of two laminse extending upwards on the
sides of the cartilaginous septum of the nose. The inferior edge
exhibits a flat surface with a raphe in the middle line, which
articulates with the superior maxillaries proper, i. e., with the
part behind the anterior palatine foramen ; and which narrows
to an edge behind, where it comes in contact with the palate-
bones. But this surface ceases abruptly in front, and only
the lamina bounding the groove for the cartilage is prolonged
on the intermaxillary part of the palate (fig. 3). In the adult
state both the scooped projection lying on the intermaxillaries,
and the remains of the surface for articulation with the supe-
rior maxillaries, can be seen, when the vomer still admits of
being accurately disarticulated. But this is not often, as it
soon becomes anchylosed with the neighbouring bones ; and
even when this has not happened, it requires that portions of
the other bones be sacrificed for the sake of removing it en-
tire. As the face elongates, the upper part of the vomer
undergoes much alteration ; not only is there a considerable
development of lamina in the mesial plane beneath the groove,
but usually tbe laminse bounding the groove deviate from the
mesial line, and one of them becomes more developed than the
other, and is more extensively anchylosed with the central
plate of the ethmoid, which, growing downwards, replaces the
cartilage between them. In consequence of these changes
taking place at a comparatively early period, the specimens
which are sold with disarticulated skulls, and from which the
descriptions in text-books are drawn up, are seldom complete,
and have most frequently more or less of the central plate of
the ethmoid adherent to them. Thus the vomer is described
as exhibiting at its upper and back part a cul-de-sac for the

Vomer in Man and the Mammalia.

7

rostrum. Such a cul-de-sac is often seen, but the central plate
of the ethmoid invariably enters into its formation, for it is
only the ethmoid, and never the vomer in the slightest degree,
which replaces the cartilaginous septum.

Explanation of Plate V.

i

Fig. 1. The vomer and lateral masses of the ethmoid of a lamb, seen from
below, a, The inferior margin of the vomer, rough posteriorly, for articulation
with the maxillaries, and smooth in front, where it comes in contact with the
intermaxillaries ; b b, the grooves which complete the nasal foramina; of the
palate bones. The spaces between the grooves and the margins of the vomer
represent the ethmo-vomerine lamina;, and on the outer aspects of the grooves
are the small orbital surfaces of the ethmoid.

Fig. 2. The vomer, ethmoid, sphenoidal spongy bones, and left palate and
maxillary bones, from the skull of an infant; seen from behind (slightly en-
larged). a, Orbital plate of the ethmoid; b , posterior extremity of the vomer;
c, sphenoidal process of the palate bone; d, orbital surface of the palate
bone, and immediately above it is the orbital portion of the sphenoidal spongy
bone. Between the two processes of the palate bone is the spheno-palatine
foramen, completed above by the inferior portion of the sphenoidal spongy
bone, e, The superior portion of the sphenoidal spongy bone.

Fig. 3. Another view taken from the same specimen : a, b, c, The parts of
the inferior margin of the vomer for articulation with the palate, maxillary,
and intermaxillary bones respectively ; d, inferior aspect of the sphenoidal
spongy bone; e, orbital plate of the ethmoid seen in perspective; /, inferior
turbinated process of the ethmoid.

Fig. 4. Illustrates the articulations of the vomer in the rabbit. Above are
the vomer and ethmoid forming one bone. Beneath are the bones of the upper
jaw of the left side, and a portion of the intermaxillary bone of the right side
adhering to it. a, Anterior extremity of the vomer, grooved for the cartila-
ginous septum of the nose ; b, the part of the vomer which articulates with c,
the extremity of the expanded mesial processes of the intermaxillary bones,
forming turbinations in connection with Jacobson’s organ.

.

P1ATI A'

Voi.n

Royal Fla'sira.l Society, Edinburgh .

H.MVarlojic.'Zi0,r £i,„Z

Fy. 4.