They are scattered irregularly throughout the middle coat.
Sometimes the intima and the adventitia also contain sparsely
distributed muscle-cells. The arterial muscular coat is dis-
tinctly separated from the intima by the interposition of the
internal elastic coat. Externally a sharp boundary is formed
either by the adventitia or by the external elastic coat. The
latter appears as a separate membrane in arteries of small and
medium size. There are, however, exceptions to this rule. The
external elastic coat consists of a close network of delicate
FIG. 69. Longitudinal section of pulmonary artery. Mounted in glycerine and acetic acid after de-
siccation of the artery, o, Internal portion of intima ; 6, external portion of intima ; c, internal elastic
coat ; d, media, showing cross sections of muscle fibres and elastic tissue ; e, adventitia.
elastic fibrils, anastomosing with similar adventitial reticula.
The adventitia is composed of interlacing bundles of connec-
tive tissue, commingled with elastic lamellae of varying thick-
The veins. From their origin in the capillaries to the point
where they enter the trunk proper, the veins preserve through-
out a uniform type of structure. But no sooner have they
penetrated into the visceral cavities of the body than we find
them undergoing considerable alterations, which may either
increase or diminish the complexity of their structure (Ran-
vier). The veins are far more numerous than the arteries.
They are also, as a rule, wider and more dilatable, and have
thinner coats. It is owing to the latter peculiarity that the
MANUAL OF HISTOLOGY.
color of the blood is seen through their semitranslucent walls.
Finally, they branch more frequently than the arteries. Three
main coats or tunics enter into the composition of most veins.
These resemble the corre-
sponding arterial struc-
tures, and have likewise
received the names of in-
tima, for the internal endo-
thelial lining ; media, for
the middle muscular ; and
adventitia, for the external
Veins, however, differ
from arteries in the feebler
development of their mus-
cular coat, in the compara-
tive paucity of elastic ele-
ments, a greater laxity
of their intima, and the
presence in some of valves.
We may distinguish veins of smaller calibre, or venules,
from the vessels of medium and large size. The venules, like
the arterioles, in certain respects resemble the capillaries. As
FIG. 70. Portion of innominate vein of dog, after in-
jection of a solution of silver nitrate. The endothelial
cells and their nuclei are visible. The media shines
through this layer.
FIG. 71. Arteriole and vennle from child's mesentery, treatment by acetic acid and glycerine: A, ar-
tery ; a, nucleus of muscle-cell of media ; ft, same in transverse section (optical). B, vein ; c. nucleus of
connective tissue constituting media, which in these minute veins contains no muscle-cells ; tf, nucleated
it may become important to differentiate the minuter forms
of vessels, we will here briefly indicate the main points of dis-
tinction between full-sized capillaries, small veins, and arte-
rioles. In the latter, the endothelial cells are more nearly
fusiform, longer, and somewhat narrower than in the venules.
In the capillaries, their form and dimensions hold an interme-
diate position between the arterial and venous types. The
middle coat is entirely wanting in capillaries, and is much less
conspicuous in the small veins than in the arterioles. In fact,
under ordinary circumstances, the muscle-coat forms by far the
most characteristic distinguishing feature between these ves-
sels. Venules quite frequently have only a few sparsely scat-
tered muscle-cells, in place of the continuous muscular layer
which exists in minute
arteries. The former
also are either altoge-
ther deficient in the in-
ternal elastic coat, or the
presence of this struc-
ture is barely indicat-
ed by delicate elastic
fibres ; these latter usu-
ally have a longitudinal
direction. On the other
hand, arteries of corre-
sponding calibre are
mostly furnished with
a distinct elastic inner
coat. Finally, with re-
S*ard tO the adventitia
we find it more highly
developed proportionally in venous than in arterial vessels,
whereas capillaries commonly have only a few faint fibres to
denote the presence, in them also, of this coat.
The internal elastic coat of the larger and largest veins is
very feebly developed in comparison with that of the arteries.
Distinct fenestrated membranes are scarcely ever encountered.
Veins are likewise possessed of an internal fibrous layer, but
here again we observe that comparatively feeble development
of a coat which in the arteries is quite conspicuous.
Among the many special characteristics of the various
veins in different regions, we will only mention the following :
the jugular veins show well-marked elastic reticula, the meshes
of which contain sparse muscular elements. In the femoral,
FIG. 72. Longitudinal section of popliteal vein : r/, tritium ;
158 MANUAL OF HISTOLOGY.
brachial, and subcutaneous branches there is a media of con-
siderable dimensions. The inferior vena cava has, in addition
to a transverse layer of muscle-cells, a longitudinal one of
greater thickness, and, besides these, contains muscle-cells,
which are scattered through its elastic coat. The veins of the
meninges of the encephalon and cord, the retina, the bones,
and the muscles, and the jugular, the subclavian, the innomi-
nate, and the thoracic portion of the vena cava are all entirely
devoid of a true muscular coat. The veins of the gravid ute-
rus have only longitudinal muscle-elements. In addition to an
outer longitudinal layer, the vena cava, the azygos, the renal,
the hepatic, the internal spermatic, and the axillary veins pos-
sess an inner circular layer. The iliac, the femoral, the popli-
teal, and several other veins contain a middle coat of transverse
muscle-cells, between internal and external longitudinal layers.
The valves of the veins consist of longitudinal bundles of
connective tissue commingled with scanty elastic fibrils, and
containing nucleated cells. The inner endothelial layer appears
to be a direct continuation of the intima of the vein. That
portion of the subendothelial tissue which does not face the
blood-current is less developed than the part turned toward it ;
the elastic fibres of the latter are also barely visible. The at-
tached valvular border frequently presents transversely dis-
posed muscle-elements. Eberth has denied their occurrence,
but they have been repeatedly observed by Banvier and other
Peculiar vascular structures. The following structures are
remarkable for the conspicuous and characteristic development
of their blood-vessels the vascular membranes, tunicw vascu-
losce, such as the pia mater of the brain and spinal cord, and
the choroid coat of the eye. In these we find that the excessive
vascularity is intended to nourish, not the membranes them-
selves, but the organs which they invest.
Blood-vascular glands, vascular plexuses. In man, two
bodies of peculiar structure represent this group. They are
the coccygeal gland of Luschka, and a rudimentary organ
called the inlercarotid gland. Both consist essentially of con-
voluted blood-vessels and nerves, imbedded in a nucleated con-
nective-tissue stroma. The coccygeal gland is a small, rounded,
pinkish body, of rather firm consistence, and is connected by a
pedicle with the middle sacral artery. This pedicle contains
blood-vessels and nerves. The arteries entering the gland-like
body become convoluted, and show numerous tubular, fusi-
form, or ampullar dilatations. Sometimes they have terminal
sacculi, closely resembling minute aneurisms, and giving the
organ its glandular appearance. Indeed, Luschka has called
them gland-tubules and vesicles. After death they are com-
Fio. 73. Section of a naturally injected coccygeal gland : a, vessels ; B, collection of cells. Eberth.
monly found to be empty, but by proper management a good
natural injection with blood may be readily obtained. Both
capillaries and veins also present lateral varicosities, studding
them in great number. All these vessels have the usual endo-
thelial lining. External to this there appear aggregations of
rounded or polygonal cells. They are furnished with nuclei,
and receive an investment corresponding to the vascular ad-
MANUAL OF HISTOLOGY.
ventitia, but containing comparatively more nuclei than that
The inter carotid gland differs from the coccygeal in its
larger size, and because it contains accumulations of ganglionic
nerve-cells. These are derived from the carotid plexus. Here
the vascular sacculi also more nearly resemble dilated capilla-
ries, whereas in the other body they approach the arterial type.
In all other respects the structure of these vascular plexuses
is identical. Some authors regard the spleen and the supra-
renal capsule as belonging to this group of blood-vascular
glands. The author sees no necessity for so considering them,
and the subject may
therefore be dis-
missed without fur-
sa. They consist in
great part of dilated
ly of the venous
type. These inter-
freely, and when
filled with blood
cause the organ to
assume the peculiar
condition known as
erection. The penis and the clitoris are supplied with caver-
nous bodies. The urethra of the female and the vestibule also
contain them. Interlacing bundles of muscle-fibres, together
with similar bands of connective tissue, form a framework for
the support of the vascular structures mentioned. The latter
present the ordinary endothelial lining.
Several years ago Dr.H. J. Bigelow succeeded in demon-
strating the existence of cavernous tissue in the nasal fossae.
In a letter to the author, Dr. Bigelow states that his point
was " the demonstration of an abundant and true cavernous
structure and erectile tissue on and about the turbinated bones,
occupying the place of what had been previously supposed to
be only venous sinuses, the loops of Kohlrausch. The new re-
sult obtained was due to a different mode of preparation. Kohl-
p IG . 74. A, cellular vascular sheath, from the coccygeal plexus :
a, connective tissue with scattered cells f nd nuclei ; fc, round and
polygonal cells lying immediately upon the capillary wall, c ; B, a
capillary from the coccygeal plexus, with a vascular sheath very rich
in cells. References as in A. Eberth.
rausch injected from the jugular vein ; I [Dr. Bigelow] inflated
the tissue locally, as if it were in the penis."
Vasa vasorum, lymphatics, and nerves. Nutrient ves-
sels are found in the walls of all the larger arteries and veins,
where they occupy the adventitia. Sometimes they are seen
to dip down into the outermost portions of the media. Lym-
phatics occur as clefts or spaces between the various tissues of
all arterial and venous trunks. Some vessels are ensheathed
by a lymphatic membrane, which is sometimes furnished with
a lining endothelium. Such structures are called perivascular,
or, better, circumvascular spaces. They may be found in
connection with the omental and the mesenteric vessels, also
the splenic and the hepatic arteries, as well as certain menin-
geal vessels of the brain and cord.
Nerve-fibres are seen to pass to many of the blood-vessels.
They enter the adventitia, and at its internal boundary sud-
denly appear to divide into numerous filaments, the ultimate
distribution of which has not hitherto been satisfactorily ascer-
tained. They seem to terminate in the muscle-cells of the
media. Beale considers the presence of ganglion-cells in the
vascular nerves as of constant occurrence. The author cannot
admit the truth of this general statement, having discovered
such cells in only exceptional instances. There is no discerni-
ble difference of structure between the vaso-constrictor and the
In addition to the well-known standard treatises by Bichat, Kolliker, Henle,
Sappey, Krause, Frey, Leydig, Teichmann, Strieker, Klein, Ranvier, Donders, Vier-
ordt, Luschka, Pouchet et Tourneux, the following may be consulted :
LUDWIG. De arteriarum tunicis. Lipsiae, 1739.
RAUSCHEL. De arteriarum et venarum structura. Vratisl., 1830.
EOBIN. Sur la structure des arteres. Compt. rend. 1847.
SCHULTZE. De art. struct. Gryph., 1850.
REMAK. Hist. Bemerk. ueber d. Blutgefasswande. Mailer's Arch., p. 96. 1850.
SEGOND. Syst. capillaire sanguin. Thse. Paris, 1853.
REMAK. Entwickelung d. Wirbelthiere. Berlin, 1855.
REMAK. Klappend. Venen. Deut. Klinik. 1856.
HACKEL. Muller's Arch. 1857.
LUSCHKA. Virch. Arch. XVIII.. p. 106. 1860.
162 MANUAL OF HISTOLOGY.
HOYER. Arch. f. Anat., p. 244. 1865.
KLEBS. Virch. Arch. VoL XXXII., p. 172. 1865.
AEBY. Med. Cent. Zeit. No. XIV. 1865.
CHRZONSZCZEWSKY. Virch. Arch. Vol. XXXV. 1865.
EBERTH. Virch. Arch. Vol. XLIII., p. 136, and Centralblatt, p. 195. 1865.
AUERBACH. Virch. Arch. Vol. XXXIII. 1865. Med. Cent. Zeit. No. X.
GIMBERT. Structure et texture des arteres. These. Paris, 1865. Journ. de
1'anat. et de la phys. Kobin, p. 536. 1865.
FASCE, LUIGI. Istologia della arterie. Palermo, 1865.
LANGHANS. Virchow's Arch. Vol. XXXVI. , p. 197. 1866.
His. Die Haute uud Hohlen d. Korper's. Basel, 1866.
LEGROS. Journal de 1'anat. et de la phys. No. III. , p. 275. 1868.
TOLUBEW. Beitr. z. Kennt. d. Baues u. d. Ent d. Capill. Arch. mikr. Anat., p.
ZIEGLER. Exp. Unt. ueber d. Herk. d. Tuberkelelemente. Wurzburg, 1875.
ZIEGLER. Unt. ueber pathol. Bind. u. Gefassneubildg. Wurzburg, 1876.
KOLLIKER. Entwickelungsgeschichte. Leipzig, 1876.
DISSE. Arch. f. mikros. Anat. Vol. XVI., p. 1. 1879.
ILLTMANN. Arch. f. mikros. Anat. Vol. XVI., p. 111. 1879.
THE LYMPHATIC SYSTEM.
BY DR. W. R. BIRDS ALL, NEW YORK CITY.
HISTOLOGICAL research has brought to light within recent
years no more important or interesting facts than those con-
nected with the lymphatic system ; interesting, in exhibiting
entirely new features in tissues which had previously been
carefully studied ; and important in their physiological, and,
particularly, in their pathological relations.
Assisted by experimental pathology, it is still in this direc-
tion that we are to look for advancement in pathological his-
tology, for there can be no doubt that heretofore too little,
attention has been paid to the lymphatic system, both in its
histological details and in its topographical anatomy.
Present condition of the mews on the structure of the lym-
phatic system Relations to the connective tissues. Unfor-
tunately we have still a great variety of contradictory observa-
tions, and various interpretations of the same observations.
Through this maze of uncertainties it is not easy to lead the
student to a settled opinion, nor can all the phases of this many-
sided subject be presented. It shall be our aim, however, to
draw the outlines. If the student wishes to follow out the
controversies, he will be aided by the references which are
appended to this chapter.
It may be said that we have, to a great extent, returned to
the views of the older anatomists and physiologists, and be-
lieve that the whole connective- tissue formation is a network of
channels ; that its interstices are, directly or indirectly, con-
nected with the lymphatic capillaries and larger vessels ; that,
in short, the lymphatic system is pre-eminently a connective-
'tissue circulatory system, irregularly distributed, it is true, but
1G4 MANUAL OF HISTOLOGY.
found in one form or another wherever this tissue exists, and
constituting in the serous membranes a great absorbent sys-
tem, with its special connections, the lacteals, the lymphatic
nodes or glands, and the fat-tracts. The important patho-
logical processes, both acute and chronic, connected with these
membranes are due principally to the fact that they are parts
of this great lymphatic system.
Of course we must not lose sight of the connections of the
latter with the complimentary blood-vascular system ; the ten-
dency has been too much in the opposite direction, however,
and this more extensive, though less visible, system has been
too often neglected in favor of its more prominent companion,
in the consideration of processes of nutrition and of patho-
General histology of the lymphatic system Previous
ideas. In describing the lymphatic system, only its general
histology will be considered, the details of its special distribu-
tion and arrangement being classed with the description of the
different organs with which it is associated. Since the serous
membranes have come to be regarded as important parts of the
lymphatic system, being, in fact, great membranous expansions
of that system, they are naturally and easily considered in con-
nection with each other. It is not intended to treat of them
here in their special details, but merely to make a general his-
tological study of them as a class. It is convenient to begin
with them in taking up the study of the origin of the lymphatic
With Yirchow originated the theory that the starting-point
of the lymphatics is from hollow anastomosing cells, the con-
nective-tissue cells, whose prolongations communicate to form
continuous tubes. He termed them plasma cells. Kolliker
supported this doctrine, and a similar view was held by Ley-
dig. Henle held a different opinion, whilst Briicke and Ludwig
reverted to the ancient theory of Bichat, that the interstitial
spaces of the connective tissue are the true sources of the lym-
phatics. Recklinghausen, introducing nitrate of silver as a
reagent, showed that the lymphatic vessels are lined, and the
serous membranes covered, with flat cells, forming an endo-
thelial layer. He observed the passage of milk and fine gran-
ules, through openings in the central tendon of the diaphragm,
from the peritoneal to the pleural surface. He believed also
THE LYMPHATIC SYSTEM. 165
that lie had discovered a system of canaliculi in connective tis-
sue, which he termed sap or juice canaliculi (saftkanalchen).
His views, as modified somewhat later, are, that the connective
tissue is traversed by serous canaliculi or plasmatic channels
which are directly continuous with the lymphatic vessels.
"Not mere fissures in the connective tissue, but interstices of
the fibrous fasciculi and lamellse of connective tissue, cemented
to one another by a tenacious, homogeneous, firm material, in
which the serous canaliculi are buried."
The lymphatics of the mesentery. A portion of the mesen-
tery between the'trabeculse, taken fresh from a cat and stained
with nitrate of silver, exhibits on both surfaces an endothelial
layer, the cells of which possess an irregular outline, marked
by the deposit of silver, either in a supposed intercellular sub-
stance or in crevices between the cells. Sometimes this outline
is polygonal, sometimes sinuous, crenated, or even sharply den-
tated. It may be an even, fine line, or it may possess irregu-
larities as if beaded. At the union of these lines, that is, where
two or more cells terminate, a round, irregularly triangular, or
spindle-shaped spot may be often observed, which is stained
like the intercellular line, or in a lighter or darker shade.
There are other spots of larger size, presenting the appearance
of openings ; we shall refer to them again. The surface of the
cells may be clear, or granular, sometimes it is quite dark, vary-
ing with the degree of staining and the condition of the tissue ;
a nucleus can usually be seen at a slightly deeper level. This
is plainly visible in unstained or slightly stained specimens, or
where special reagents have been used to make the nuclei promi-
nent, as hsematoxylin or picro-carminate of ammonia. The
granular appearance spoken of is sometimes confiiled to a series
of cells which surround a stoma, or the black spots mentioned,
while the neighboring cells may be clear ; in other cases, sev-
eral corpuscles in the form of an irregular tract may present
Klein has observed cells which are club-shaped, undergoing a budding pro-
cess, i.e., giving off little bodies resembling lymphoid corpuscles. He has given
the term germinating endothelium to these cells. Other histologists have made
Underneath and around the nuclei a delicate, intricate, re-
ticulum of elastic fibres may be seen plainly in unstained speci-
166 MANUAL OF HISTOLOGY.
mens, and by careful focussing in silver preparations. Accord-
ing to Ranvier, they are connected near their point of union
by a very thin, elastic, fenestrated membrane. Below the layer
of elastic fibres is the connective tissue which forms the basis
of the membrane. It consists of fasciculi, which are straight,
or wavy, according to the degree of tension of the membrane,
or its fasciculi are held together by the elastic fibres, which
penetrate from the reticulum on each side. They usually pre-
-sent a decidedly convoluted appearance in ordinary specimens,
and in consequence of the contiguous fasciculi not possessing
corresponding convolutions, clear interspaces are seen. Some-
times the fibres are very irregular in their arrangement. Ran-
vier claims that an interfascicular membrane can be demon-
strated here also. Ordinary flat, branching connective-tissue
cells are distributed through this tissue ; they lie upon and
between the fasciculi ; they are particularly numerous under
the endothelial layer. Lymphatic and blood- capillaries trav-
erse the interspaces and run upon the fasciculi. In the mesen-
tery and pleura they form a wide -meshed plexus ; in the peri-
cardium a close plexus.
To see the features of the deeper portions to advantage, we
must remove the superficial endothelial layer before staining
Kleirts method of studying the omentum. Klein has de-
scribed a very careful process for doing this, and as he claims
it must be followed in detail to obtain the results at which he
has arrived, we reproduce it : "To prepare the omentum, a rab-
bit is killed by bleeding ; the stomach is exposed ; after having
pushed the intestine to the right side, the free surface of the
omentum is pencilled several times from the large curvature
toward the diaphragm, with a fine camel's-hair pencil moistened
with fluid of the abdominal cavity. After that, a J or \ per
cent, solution of nitrate of silver is allowed to flow over the
omentum from a large capillary -tube until the membrane has
become slightly milky (one or two minutes are generally suffi-
cient) ; after that, the stomach, together with the omentum,
spleen, pancreas, and a portion of the duodenum is cut out and
transferred to a large capsule with distilled water ; after some
time the water is renewed and the omentum is separated under
water, together with the spleen and pancreas, from the stomach,
with scissors, and is transferred to common water. Those parts
THE LYMPHATIC SYSTEM. 167
of the omentum which are seen to contain small patches are cut
out and mounted A failure is more frequent than a
success. Either the surface has not been pencilled enough,
and then the endothelium of both surfaces is colored, and
consequently, hardly anything is to be seen of the cellular
elements of the ground-substance ; or the surface has been
pencilled too hard, and then the arrangement of the ground-
substance is altered, its bundles appear considerably stretched
and distinctly fibrillar."
When these patches referred to, found in the mesentery,
and particularly in the omentum, are examined, they are ob-
served, according to Klein, to consist of systems of somewhat
flattened, finely granular, nucleated, branched corpuscles con-
nected together ; the spaces which appear clear between them
forming the lacunae and canaliculi, corresponding to Reckling-
hausen's lymph canalicular system. The nuclei of these cells
are sharply defined, oval, and possess one or two nucleoli.
Lymphoid corpuscles are found in these spaces, and also
slightly larger corpuscles, which are supposed to be derived,
in part, at least, from the branched cells by a process of bud-
ding. Klein calls these patches lympTiangeal patches or nod-
ules, and lympTiangeal tracts. He divides them into two