The =thoracic duct= arises from a small cisterna chyli and is very
variable. It is exceptional to find a single trunk throughout, as is
often the case in the horse. The duct is largely covered by fat and
small lymph glands. There are often two ducts, one on either side of the
aorta, which may join at a variable point or terminate close together at
the junctions of the jugular and brachial veins. In other cases the duct
is single for a variable distance, then bifurcates or divides into three
or four branches, which are often connected by plexiform anastomoses.
The efferent vessels from the intestine converge to a large trunk which
accompanies the anterior mesenteric artery and vein. It passes below the
pancreas and receives usually a large duct which is formed by efferent
vessels from the stomach, liver, and spleen; this duct sometimes opens
directly into the cisterna. The gastro-intestinal trunk receives the
collecting duct (truncus lumbalis) of the lumbar lymph vessels, forms a
bend around the right renal vessels, and joins the cisterna.
The =lymph glands= in the ox are in general less numerous but larger
than those of the horse, and in some situations a single large gland
occurs instead of a group of smaller ones, as found in the latter
animal.
The =submaxillary lymph glands= are usually two in number, right and
left; each is situated under the external maxillary vein between the
submaxillary salivary gland and the sterno-cephalicus muscle. Usually
one or two hæmolymph glands are near it. There is generally a small
gland on the deep face of the anterior part of the submaxillary salivary
gland, and small nodes may be found further forward in the submaxillary
space.
A large =subparotid lymph gland= lies on the postero-superior part of
the masseter muscle, partly under cover of the upper end of the parotid
gland. Several hæmolymph glands lie on its deep face.
The =pharyngeal lymph glands= number two or three on each side. Of
these, two large =suprapharyngeal glands= (Lg. retropharyngeales) are
situated about an inch apart between the dorsal wall of the pharynx and
the ventral straight muscles (Figs. 281, 365). These are two to three
inches long. Enlargement of them is likely to cause difficulty in
swallowing and in respiration. Behind these are several hæmolymph
glands. An =atlantal gland= is situated below the wing of the atlas on
the spinal accessory nerve. It is discoid, oval in outline, and may be
an inch and a half or more in length. It is partly covered by the upper
end of the submaxillary salivary gland.
A smaller lymph gland (parapharyngeal) is usually found along the lower
border of the carotid artery (_i. e._, ventral to the atlantal gland) on
the lateral wall of the pharynx and under cover of the submaxillary
salivary gland or at its posterior border.
Two or three small =anterior cervical lymph glands= commonly lie along
the carotid artery a little further back.
The =middle cervical lymph glands= comprise a series of small nodes
along the dorsal face of the trachea.
In the sheep and goat there is a lymph gland at the middle of the
neck, in the angle between the spinalis and complexus, covered by the
splenius. It receives vessels from the atlantal gland and sends
efferents to the prescapular gland.
The =prescapular= or =superficial cervical lymph gland= is situated at
the anterior border of the supraspinatus under cover of the
mastoido-humeralis and omo-transversarius. It is elongated and may be an
inch or more in width and four or five inches long. Two occur in
exceptional cases.
A chain of hæmolymph glands lies along the front of the shoulder,
covered above by the trapezius. Others are frequently found (in the
calf especially) on the surface of the omo-transversarius at the point
where it passes under the mastoido-humeralis (Forgeot).
[Illustration:
FIG. 478.—SUPERFICIAL LYMPH GLANDS OF COW PROJECTED ON SURFACE OF
BODY.
_1_, Submaxillary; _2_, subparotid; _3_, atlantal; _4_,
parapharyngeal; _5_, anterior cervical; _6_, middle cervical; _7_,
prescapular; _8_, precrural. (With use of fig. in Ellenberger-Baum,
Anat. f. Künstler.)
]
The =posterior cervical= or =prepectoral lymph glands= number commonly
three or four on each side. One or two are placed on the brachial
vessels, one below the brachial vein at the first rib, and one at the
junction of the common trunk of the external and subcutaneous thoracic
veins with the brachial.
The =intercostal lymph glands= are situated, as in the horse, at the
upper parts of the intercostal spaces. Associated with them are
hæmolymph glands.
The =sternal lymph glands= are situated along the course of the internal
thoracic artery at the lower part of the intercostal spaces. The largest
is close to the thoracic inlet. Several glands occur in the fat about
the apex of the pericardium.
4. Several =anterior mediastinal lymph glands= are placed along the
œsophagus and the trachea.[183] Hæmolymph glands occur here also.
Usually three large =bronchial lymph glands= are present (Fig. 289). One
is situated at the origin of each chief bronchus and the third is under
the trachea at the origin of the special bronchus of the apical lobe of
the right lung. Another may lie between the aorta and the left branch of
the pulmonary artery. These glands are often pigmented. Other small
nodes are situated on the bronchi within the lungs.
The =posterior mediastinal lymph glands= comprise two or three of large
size placed along the dorsal wall of the œsophagus. There may be a
single gland about eight inches (ca. 20 cm.) long, the anterior half of
which lies on the œsophagus (Fig. 289).[184] A small gland is situated
in the acute angle formed by the posterior vena cava and the diaphragm.
A single =axillary lymph gland= is situated on the distal part of the
teres major on the course of the vein from the latissimus dorsi.
The =lumbar lymph glands= form an irregular series scattered along the
abdominal aorta and posterior vena. A bean-shaped =renal lymph gland=
occurs at the hilus of each kidney. Hæmolymph glands occur along the
course of the aorta.
[Illustration: