such as the mammary and salivary glands,
derive their nerves chiefly from cerebro-spinal
nerves.
From the experiments of SchifF and others
it would appear, however, that the ganglionic
system of nerves is more intimately con-
nected with these processes than the strictly
cerebro-spinal nerves are. Thus, SchifF found,
in regard to the fifth nerve, that when it was
divided between the brain and Gasserian gan-
glion, the destruction of the textures of the
eyeball follow more slowly then when it is
divided between the ganglion and the eye.
In the frog, also, when the lumbar plexus was
divided, the animal continued for two or three
months without any disturbance being ob-
served in the nutrition of the limb ; but when
several of the lumbar ganglia were removed,
dropsical effusion into the abdominal cavity,
and inflammation of the peritoneum, ending in
the death of the animal, ensued in the course
oftwoweeks.f Axmann , as quoted by Va-
lentin, divided at their roots the nerves which
supply the posterior extremity in the frog,
but in no instance observed that the opera-
tion was followed by any disturbance in the
nutritive processes : wounds of the soft tex-
tures as well as of the bones healed as rapidly
* De vi motoria basios encephali, p. 37., as
quoted by Valentin.
t Op. cit. p. 37.
f T Ganglioruni Systematis Structura peitiri
ejusque Functionibus. Berlin. 1K<1~. > MX
TEGUMENTARY ORGANS.
473
ES in the sound leg. When he divided the
trunk of the lumbar nerves below the spinal
ganglia the skin became gradually pale, its
pigment cells diminishing to mere points ; the
structures softened ; the liver and kidney no
longer secreted ; while dropsicaL effusions,
containing the elements of the bile and uric
ncid, at the same time took place. The blood
corpuscles also gradually disappeared. The
vessels of the spinal cord and of its mem-
branes became very much distended with
blood. When the lower portion of the sym-
pathetic cord on either side was removed, the
blood-vessels of the hind leg and pelvic organs
became highly congested ; the contractility of
the muscular tissue in the legs and in the
pelvic organs disappeared. Blood was ex-
travasated into the bladder and rectum, secre-
tion of urine ceased, and dropsical effusions
took place. The circumstance that section of
sensory nerves is followed by derangement in
the nutritive processes much more quickly
than similar lesions of motor nerves is also ex-
plained by Volkmann as due to the fact of
the former containing a comparatively larger
number of fine or sympathetic fibres.
BIBLIOGRAPHY. Willis, Cerebri Anatomia
Nervorumque Descriptio, Amster. 1683. Pourfour
du Petit, Mem. de 1'Academie, des Sc. de Paris,
1727, p. 3. Bergen, Dissertatio de Nervo inter-
costal!, 1731 ; also in Haller, Dissert. Anat. torn. ii.
p. 871. Haller, Respic. H. G. Taube, De vera
Xervi intercostalis Origine, Getting. 1743. Disput.
Anat. torn, ii., et in Opera Minora, torn. i. Huber,
Epist. Anat. ad Wigaud, De Xervo intercostali, &c.,
Getting. 1744. Neubauer, Descript. Anat. Nervo-
rum Cardiacorum, Frankfort et Lips, 1772. C. G.
Andersch, Frag. Descript. Xerv. Cardiacorum, Lud-
\vig Script. Xeurol. vol. ii. Johnstone, Essay on 'the
Ganglions, 1771. Haase, Dissertat. de Gangliis
Xervorum, Leips. 1772, Iwanoff, De Origine
Nervorum intercostalium, Argent. 1780; also in
Ludwig, Script. Xeurol, vol. iii. Ludwig, De Plexu-
1ms Xervorum abdominalium atque Xervo intercos-
tali Observations, Leips. 1772 ; also in Script.
Xeurol. Wrisberg, Observat. Anat. de Xervis Viscer.
abdomin. in Ludwig. Script. Xeurol., torn. iv. p. 27.
Scarpa, Anat. Annat, lib. L, De Gangliis et Plexu-
bus nervorum, Modenae, 1779, in 4to. Tabulae
Neuiologicae ad illustrandum Historian! Anat.
cardiacorum Xervorum, &c. Paviae, 1794. W. Hun-
ter, Anatomical Description of the human Gravid
Uterus, and its Contents, London, 1794. Watiher,
Tabula? Xervorum thoracis et abdominis, Berlin,
1783, in fol. Gerrardi, De Xervo intercostali,
Florence, 1791 ; also in Script. Xeurol, torn. iii.
Sommering, De Corporis humani Fabrica, torn. iv.
p. 334. Portal, Description du Xerf intercostal dans
1'Homme, Mem. de 1'Institut. Xational, torn. iv.
p. 151. Munnicks, Observat. Variae, Groning, 1805.
Rail, Ueber die Eigenschaften des Gangliensystems
und sein Verhaltniss zum Cerebralsystem, Reil's
Archiv. Band. vii. Rudolpki, Einige Bemerkungen
iiber den Sympathischen Xerven, Abhandlungen
der Berliner Academic, 1818, et 1815-16. Ribes et
Ouiiissier, Rech. Anat. et Physio). Mem. de la
Socie'te Me'dic. d'Emulation, torn. vii. p. 86. Bock,
iiber das Gangliensystem, Abhandlungen iiber das
fiinfte Xerven paar, 'Meissen, 1817. Weber, Ana-
tomia comparata Xervi sympathici, Lips. 1817.
Dapny, Observat. et Experiment, sur 1'Enlivement
des Ganglions gutturaux, des Xerfs trisplanch-
niques sur des Chevaux, Journ. de Corvisart, 1816,
torn, xxxvii. p. 340. Wutzer, De Corporis hu-
mani Gangliorum fabrica atque usu Monographia,
Berlin, 1817. J. F. Lobstein, De Xevi sympathici
Humani fabrica, usu et Morbis, Paris, 1823. L.
Hirzel, Dissert, sistens nexus Xervi sympathici
cum Xervis cerebralibus, Heidelberg, 1824, 4 to. ;
also in Tiedemann and Treviranus Zeilschrift,
Band i. p. 197. Langenbeck, Icones Anatom. neurol.
fasc. iii., Getting. 1826. Arnold, Dissert, inaug. de
Parte cephal. Xervi s}*mpathici in Homine, Heidel-
berg, 1826, 8vo. ; also'in Tiedemann und Treviranus,
Zeitschrift fur Physiol. Band ii. Arnold, Der
Kopftheil des vegetativen Nervensystems beim
Menschen in Anat. und Physiol. Hinsicht bearb.
Hiedelberg, 1830, 4to. Tiedemann, Tabulae Xervorum
Uteri, Heidelberg, 1822. Varrentrapp, Observat.
Anatom. de Parte cephalica Nervi sympathici, etc.,
Franc-fort, 1832. Bidder, Xeurolog. Beobachtungen,
mat abbild. Dorpat, 1836. Bracket Funct. du Syst.
Xerv. gangl. 1837. Van Deen, Dissert, de Dif-
ferentia et nexu inter Xervos vitae Animalis et Or-
anicae, Leyd. 1834. Giltay, De Xervo sympathico,
eyd. 183-1. Panizza, Richerche sperimentali sopra
i Xervi, littera del Profess. Panizza. al Profess.
Bufalini, Pavia, 1834. Remak, Observat. anatom.
et micros, de Systematis nervosi Structura, Berlin,
1838, 4to. C. 'Krause, Synopsis Icon, illus. Xervo-
rum Systematis Gangliosi in Capite Horn. Hanover,
1839. Bourgery, Mem. sur 1'Extremite ceph. du
Grand Sympath. Compt. Rendus, 1845. Valentin,
De Functionibus Xervorum cerebralium et Xervi
sympathici, Berne, 1839. Kiesselbach, Dissertatio
sistens Formationis ac Evolutionis Nervi sympa-
thici una cum Descriptione ejusdem Xervi decursus
in Animalibus quibusdam Vertebratis, Monachi,
1836. Krause, Synopsis Icone illustrata Nervorum
Systematis gangliosi in Capite Hominis, Hanover,
1839. Horn, Reperta quaadam circa Nervi sym-
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Illustrata, Wirceburgi, 1839. Robert Lee, the Ana-
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with plates ; and on the Ganglia and Nerves of the
Heart, Lond. Med. Gaz. Nov. 1846, &c. Jobert,
Rech. sur les Nerfs de 1'Uterus, Compt. Rendus,
Mai, 1841, p. 882. Bidder und Volkmann, die
Selbstandigkeit des sympathischeii Nervensystems,
durch Anat. untersuch. nachgewiesen, Leipzig, 1844.
4to. Kolliker, die Selbstandigkeit und Abhangig-
keit des sympathischen Nervensystems durch Anat.
untersuch, bewiesen, Zurich, 1845, 4to. Bracket,
Consid. sur le Syst. nerv. Gangl. Compt. Rendus,
de 1'Acad. des Sc. 1845. H. C. Raddiffe, On the
Sympathetic Nerve, London, 1846. Snow Beck,
On the Structure of the Sympathetic Nerve, and its
Connections -with the Spinal Nerves, Phil. Trans.
1846. Robin, On the Ganglia, &c. of the Skate,
Compt. Rendus, 1847. R. Wagner, Sympatbischer
Nerv. Ganglienstructur, &c., Handworterbuch der
Physiologic, Band iii. F. H. Bidder, zur Lehre von
dem Verhaltniss der GanglienkorperzudenXerven-
fasern, Leipsig, 1847. C. F, Axmann, De Gang-
liorum Svstematis Structura penitiori, etc., Berlin,
1847. 4 c. Tab. Wagner, Sympath. Gangl. des
Herzens, Handwort. der Phys. Band iii. p. 452.
(J. Drunimond.')
TEGUMENTARY ORGANS. In en-
deavouring to deal with so large a subject as
the tegumentary organs of animals, within the
limits of an article like the present, it ap-
peared advisable not to attempt to enter into
minutiae of detail (which indeed fall more
properly within the province of those who
treat of the special classes), but so far as pos-
sible to regard these organs as a system in the
sense of Bichat as a sort of zoological class
whose members, the tegumentary organs of
particular animals, are but special modifica-
tions of one general plan. In reflecting how
this might best be done, however, I was met
at the outset by certain difficulties and per-
474
TEOUMENTARY ORGANS.
plexities whose solution appears to me to be
essential to any philosophical treatment of
the subject, and to the consideration of which
1, therefore, propose to devote the following
Preliminary Section.
1 . My first difficulty was to find an answer
to the question, What constitutes a tegu-
mentary organ as distinguished from any other?
The most obvious definition of an integu-
ment or tegumentary organ is, of course,
that which forms the external covering of any
animal viscus, on the other hand, being
that which is contained. More strictly, it
may be said that the integument constitutes
that free surface of an animal which is ex-
ternal to the edges of the oral and anal aper-
tures, or where the former alone exists, to its
edge. Now these definitions are perfectly
sufficient so far as surface is concerned ; but
suppose we make a section perpendicular to
the surface, where does integument cease, and
where does viscus begin ? So far as I am
aware, no elucidation of this point has hither-
to been undertaken, and yet, for want of it,
the greatest confusion prevails in the nomen-
clature of those organs which constitute the
outer wall of the animal frame.
Intimately connected with this question, and
indeed forming a part of it, is a second. In man
and the higher animals, there is an universally
recognised distinction of the integument into
two portions, the epidermis and the derma ;
and these terms have been extended to all
animals. But, if we inquire what constitutes
an epidermis, and what a derma, no definite
answer is to be met with. It may be said that
the derma is vascular, while the epidermis is
nonvascular ; or that the epidermis is a simple
cellular horny structure, while the derma is
complex and fibrous,- but these characters,
applicable enough among the higher animals,
fail completely with the lower.
Thus, in the majority of the Invertebrata,
the derma cannot be said to be vascular,
while, on the other hand, the epidermis, or
its representative, assumes the structure of
fibrous tissue, bone, cartilage, dentine, and
enamel, acquires, in fact, the utmost
complexity, and, instead of possessing a horny
nature, contains chitin, cellulose or calca-
reous salts.
Following Mr. Bowman, who, of course,
when he wrote his well-known article on
" Mucous Membrane," in this Cyclopedia,
could not contemplate the new questions to
which the progress of ten years would give
rise, many regard that which is external to
a " basement membrane " as epidermic, that
which is internal to it, as dermic structure.
This test, however, fails us where we most
want it ; for among the lower animals, and in
some integumentary organs among the higher,
membranes identical in structure, or rather
in htructurelessness, with " basement " mem-
branes, may be met with, forming the surface
of what are assuredly epidermic organs.
I believe that here, as elsewhere, the only
ultimate appeal lies to development, both as
it occurs in the embryo and as it goes on in
the adult. What, in fact, is the first process
which takes place in the embryo, when the
germinal disc is once formed ? It is a sepa-
ration into two layers, by the setting up within
the outer portion of the primitive germ of a
process of growth independent of that in the
inner portion. Where these two areae or
planes of growth, as they might be called,
meet, the germ readily separates into two
portions, the outer of which is the so-called
serous layer, the primordial tegumentary
system ; while the inner is the mucous layer,
the primordial viscus. Of course each of
these, while actually integument and intestine,
represents potentially a great deal more, the
former, for instance, in the higher animals
becoming eventually differentiated into the
proper tegumentary system and a great part
of the nervous, the muscular, and the vas-
cular systems ; but what I wish to direct
attention to at this moment, is the fact, that
this first differentiation into integument and
viscus proceeds from the setting up of two
independent lines, or rather planes of growth,
in the germinal membranes.
In the Hydra and Hydroid Polypes gene-
rally, we have the essence of this embryonic state
as a persistent condition. If, in fact, the body
or almost any organ of one of these animals
be examined, it will be found (see Memoir on
the Structure of the Medusa?, Phil. Trans.
1849) to be composed of two distinct mem-
branes, an inner and an outer (fig. 303. A).
The junction between the two is distinctly
marked by a clear line, which would elsewhere
be called a basement membrane (). External
and internal to this, there is a layer of young
tissue, consisting of a homogeneous periplast
with minute imbedded endoplasts (" nuclei").
As we proceed towards the free surface, we
find that a process of vacuolation and cel-
lulation takes place in the periplast, until the
coarsely cellular appearance with which every
one is acquainted is produced.
Fig. 303.
A, hydra ; b, outer membrane ; c, inner mem-
brane.
B, young mammal ; b, epidermis ; c, derma.
In the Hydra, then, we have the whole
thickness of the body divided into two por-
tions by a line, on each side of which, inwards
and outwards, there is an increasing histo-
logical metamorphosis or differentiation.
There is a median plane of no differentiation,
TEGUMENTARY ORGANS.
475
as it might be termed, external and internal
to which, is a zone of indifferent tissue, while,
still more remote again, is a zone of meta-
morphosed tissue. The absolute structure of the
two layers thus produced is very similar*, so
much so, that, as is well known, either may
perform for a time the function of the other.
The distinction between the integument and
the mucous membrane in a morphological
point of view, however, is as strongly marked
as in the most complex animal. The integu-
ment, in fact, grows from within outwards it
is endogenous, its youngest portions being
internal : the mucous membrane, on the
other hand, grows from without inwards
its youngest portion is external, and it is,
therefore, exogenous.
We have here, I believe, the fundamental,
and the only essential distinction, between
true integumentary or " epidermic " structures
and all others. An integumentary or epidermic
organ forms or has formed a part of the external
surface, and grows endogenously ; its youngest
portion and plane of no differentiation being
directed inwards.
If, for instance, we compare the young skin
of a mammal with the body of the Hydra, we
shall find precisely the same planes and zones.
Fig. 303. B, represents a perpendicular sec-
tion of the integuments of a fcetal lamb 3^
inches long. (A) marks the position of the line
of no differentiation separating the epidermis
from the derma ; on the outer side of that
line lie the close-set endoplasts of the deepest
layer (rete) of the epidermis, which are dis-
posed somewhat perpendicularly to the sur-
face. On the inner side are the less approxi-
mated endoplasts of the outer youngest layer
of the derma, more or less parallel to the sur-
face. From a to b, lies the epidermic area of
metamorphosis, the indifferent tissue becoming
gradually converted into flattened horny cells.
From a to r, on the other hand, is the dermic
area of metamorphosis, the indiiferent tissue
gradually changing into connective tissue.
It will be observed here, that as the whole
serous layer of the germ corresponds in struc-
ture with the epidermis only, of the fully
formed animal, so the whole integument of
the Hydra corresponds with what is usually
considered as only a portion of the integu-
ment the epidermis of the mammal. The
derma, or true skin of the latter, would not
come at all under our present definition of
integument, since it has all the morphological
characters of the mucous layer of the Hydra,
or of the germ ; i. e. its youngest layer is ex-
ternal, its growth is exogenous, and the me-
tamorphosis of its tissue takes place from
within outwards.
In fact, in all animals higher than the
Hydroid Polypes (possessing therefore a vis-
ceral cavity) we find a complication of struc-
ture, corresponding with that which is pro-
duced in the germ, when the "membrana in-
termedia'' divides into its parietal and intes-
tinal lamina?. Compared with the Hydroid
* Though not, as it is commonly said, identical.
Polypes, the higher forms are double animals,
and a section of their bodies is, morphologi-
cally speaking, like a section of two Hydra?,
one contained within the other. Both the
intestinal parietes, and those of the body, pre-
sent the same distinction into a central plane
of no differentiation, from which growth and
metamorphosis proceed inward and outward
on the two respective surfaces, as that ob-
served in the parietes of the Hydra.
The formation of this so-called membrana
intermedia, in fact, appears to result from a
repetition of the process which gave rise to
the two primary layers of the germ. The
previously central plane of no differentiation is
replaced by two others, from which growth
and metamorphosis proceed in the same way.
The result is, of course, the division of the
germ into three layers a central and two
superficial (inner and outer) planes of meta-
morphosed tissue and two planes, whence
growth and metamorphosis proceed.
It results from all this, that, among the higher
animals, the true homologue of the integu-
ment of the Hydra is the epidermic layer
alone. But it would be exceedinglyinconvenient
to change the accepted meaning of " Integu-
ment " on this ground ; and, therefore, I shall,
throughout the present article, consider as
integument the outermost plane of indif-
ferent tissue in the animal body, with its external
and internal arece of metamorphosis collectively ;
these being simply the expressions of two pro-
cesses of growth in opposite directions, and their
line of contact.
It must not be supposed that this phrase-
ology involves any hypothetical views: the fact
that' any integumentary organ consists of
these three portions will be found to be either
distinctly stated or implied by all writers,
and is indeed obvious enough on inspection.
But though the facts be old enough, this ex-
pression of them is unfortunately so new, that
I know of no existing terminology by which
it can be properly enunciated. The term
" Epidermis," ibr instance, at present, though
it denotes the important character of the
direction of growth to which I refer, implies
even more strongly the simple cellular struc-
ture of an organ ; so that to speak of " Epi-
dermic " bony or fibrous tissue would sound
almost contradictory. Again, all these distinc-
tions, which have been shown to exist between
the two elements of the integument, equally
hold good with regard to the mucous mem-
branes. Now we have a term " Epithelium "
for the epidermic element of the latter ; but
there is, as far as I know, none for the ele-
ment which corresponds v\ith the derma. Nor
have we any word for the boundary line be-
tween the endogenous and exogenous areae
of growth the term "basement membrane"
expressing only an accidental character of the
tissue immediately on one or the other sides
of that line.
Although with great reluctance, then, I feel
compelled to propose two or three new terms,
which may have general application, not only
to the integumentary organs, but to all other
476
TEGUMENTARY ORGANS,
membranes which possess free surfaces
and definite directions of growth and meta-
morphosis.
The boundary line passing through in-
different tissue between any two such op-
posite areae of growth and metamorphosis,
I term the Protomorphic line. The whole ex-
ternal (free) area of metamorphosis I call the
Ecderon ; the entire internal (deep) area of
metamorphosis, the Enderon.
It will be observed that these definitions rest
wholly upon the mode of growth, and leave
altogether out of consideration the structure
of the resulting tissue. In fact, as I have al-
ready said, an extensive study of the integu-
mentary organs convinces one at once that
mere structure affords no base for homology ;
the ecderon, for instance, presenting every
variety from the structurelessness of a homo-
geneous membrane, as in the Tseniadae, to the
complex combination of the so-called enamel,
dentine and bone, in the scales of Placoid
Fishes.
It is, I venture to think, no small evidence
in favour of the importance of these consi-
derations that they enable us to carry still
further the doctrine of the identity of struc-
ture of plants and animals sketched by Cas-
par Wolff, and developed in our own times
by Schwann. If we make a transverse sec-
tion of the growing limb of a vertebrate ani-
mal, leaving out of consideration, for the
moment, the vessels, nerves, and muscles, we
observe from the surface inwards, 1st, the
ecderonic area of metamorphosis; 2nd, the
integumentary protomorphic line ; 3rd, the
enderonic area of metamorphosis ; 4th, the
periosteal area of metamorphosis ; 5th, the
protomorphic line, formed by the indifferent
tissue between periosteum and bone ; 6th, the
osteal area of metamorphosis, within which
lies, 7th, the cartilage resulting from the me-
tamorphosis of the tissue of the primitive axis
of the limb.
Now, if we compare this with the growing
shoot of a young exogenous plant, we meet
with exactly the same series from without
inwards. There is, 1st, the epidermis, which
commonly becomes replaced by a cork or peri-
dermal layer, just as the primary epidermis
over a nail is thrust aside by the subjacent and
subsequently-formed horny matter ; or, as the
horny " epidermis" of a Skate is pushed aside
and replaced by the calcareous placoid spine.
Beneath this lies, 2nd, a protomorphic (or
cambial} line, from which metamorphosis into
periderma goes on outwards, while inwards it
passes into, 3rd, the metamorphosed tissue of
the mesophloeum. Next to this comes, 4th,
the metnmorphic area of the enclophlceum
or liber ; within which is, 5th, the proto-
morphic line of the cambium, which becomes
metamorphosed on its inner surface into, 6th,
the wood ; within which lies, 7th, the pith,
the result of the metamorphosis of the pri-
mitive axis of the shoot.
I have endeavoured to render these relations
obvious by the diagram (fig. 304.), which may
be taken for a section from centre to surface
of a foetal limb, or of an exogenous branch, a,
outer protomorphic line between epidermis or
periderma and mesophloeum in the plant ;
Fig. 304.
between ecderon and enderon in the animal ;
a', inner protomorphic line between liber and
wood of plant, between bone and periosteum
of animal ; 6, 6', cork and epidermic layers of
plant ; cellular epidermis and scale of animal,
fish, e.g. ; c, mesophloeum, enderon (derma) ;
</, liber, periosteum ; e, e' t wood and pith, bone
and cartilage ; x, axis; */, surface.
The consideration of vegetable structures
will aid us even further in understanding the
manner in which the different varieties of in-
tegumentary organs, with which we shall meet,
are formed. For it is well known that the
outer covering of a plant may ultimately be
constituted in one of three ways. 1. The
original cellular ecderon may persist un-
changed. 2. The " epiderm " persisting, a la-
minated, but otherwise structureless " cuticula"
may be developed upon its outer surface,
attaining sometimes a very considerable thick-
ness. 3. The original epidermis is cast off,
its place being taken by the development of a
new layer of different, usuallj' suberous con-
stitution, beneath it, which then goes on
growing endogenously, and constitutes the
permanent integumentary surface. Now, we
find a precise parallel for all these conditions
in animals. In the soft integument of most