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326 ANATOMY.

microscopically they resemble in many respects the white corpuscles of
the blood, but they are smaller and less uniform in size, varying from
^^ ^"*^'^^ ^^^ diameter. In addition to the lymph-corpus-
2"TFo soVt
cles there are present in almost every specimen of lymph small gran-
ules, regarded by some as free nuclei, which have a gray color and
exhibit the Brownian movement, lied corpuscles are also found, par-
ticularly in the large lymphatic trunks and in the thoracic duct.
The lymph-corpuscles vary much in size, shape, and general apjiear-
ance. Some are cpiite small, spheroidal in shape, and consist of a single
nucleus surrounded by a small quantity of protoplasmic matter. Others
are larger, and frecpiently contain several vesicular or spheroidal nuclei
which are surrounded by a limiting membrane, while the enveloping
mass of protoplasm is quite abundant. Many leucocytes contain col-
lections of granules ^v'hich are highly refractive and impart to the cor-
puscle a distinctly granular character. The lymph-corpuscles are made
up of a fine network of an albuminous material, in the meshes of which
is found a colorless semifluid substance apparently of an albuminous
character. There is no cell-wall present in any of the true lymph-cor-
puscles. Tiiey originate either by subdivision of pre-existing cells or
are developed within the lymphatic glands.
Origin of Lymphatics.—The mode of origin of the lymphatics
has until recent years been involved in the greatest obscnirity. But the
investigations of Von Recklinghausen, Klein, Ludwig, and many others
have gone far toward demonstrating the true origin of these vessels.
The following modes of origin are now well known :
1. Origin in Li/inpJi-i^j)ace.s or Jidee-canah.—Throughout the con-
nective-tissue system of the body are located immbers of small, irregu-
lar, stellate spaces which comnuniicate very freely with each other.
These are the so-called juice-canals of Von Recklinghausen, and are
su])posed to rej)resent the ultimate radicles of the lymphatic vessels.
They vary considerably in size, and their shapes are determined by the
nature of the tissues in which they are placed. They do not possess an
endothelial lining, but contain one or more connective-tissue corpuscles
which exhibit chara(;teristic amoeboid movements. As these spaces
comuuniicate very freely with each other, the movement of the lymjih
through them and around the islets of tissue readily 'takes place.
The lymph-spaces communicate directly with the Iipnph-capillnrieN,
as was also demonstrated by Von Recklinghausen. The lym])h-ca))il-
laries constitute a jilexus of fine vessels Avhich give rise to the smallest
lymj)hatic trunks ; they vary in shape according to the tissue in which
they are found, and also in size, but are always larger than the capil-
lary blood-vessels. Their walls are formed by a lining of simple endo-
thelial cells with characteristic sinuous margins.
2. Origin in Openings on the Surface of Serous Membranes.—The
large serous cavities, such as the peritoneal, pleural, pericardial, sul)-
arachnoid, etc., have been shown by Klein, A^on Recklinghausen, and
many others to comnuniicate with the lymphatic vessels. Their mode
of origin can best be studied upon the peritoneal surface of the central
tendon of the diaphragm. This surface is covered with a layer of
endothelial cells, whose sinuous margins can be readily exhibited by