The Abdominal and Pelvic Brain
Byron Robinson, M. D.


"Otie glorious hour of conquering strife is worth an age of quiet peace."

We do well what we do automatically.

    The trunk of the vaso-motor (sympathetic) nerve has experienced a variety of names:
    SYNONYMS: The lateral cords of the sympathetic; the principal cords of the sympathetic; the lateral ganglionic chain of the sympathetic; the nodular cords of the sympathetic.
    GERMAN: Grenzstrang, Hauptstrang, Knotenstrang.
    The nerve strands connecting the ganglia of the sympathetic trunk are termed commissural cords.  The trunk of the sympathetic nerve presents the form of an elongated elipse enclosing the vertebral column, united at the proximal and distal ends by unpaired ganglia.  The trunk consists of a vertical, symmetrical, bilateral ganglionated cord with indefinite union at the proximal end (ganglion of Ribes) and distal ends (Ganglion Coccygeum).  The number of ganglia and roots correspond in general to the number of spinal nerves.  Exceptions occur in which the ganglia coalesce, as in the reduction of the seven cervical to the usual number of three.  The total number of trunk ganglia (3, cervical), (11, dorsal), (4, lumbar) and (4, sacral) vary from 20 to 25.  The form of the trunk ganglia varies and may be elongated, olive, spindle, triangle, pyramidal, irregular shaped.  The ganglia in general are located ventral to the transverse processes and on the lateral surfaces of the vertebrae.  However, the relation of the ganglia in each segment to the vertebra varies.  The trunk ganglia vary in dimension from 3/4 of an inch long (inferior cervical ganglion) to less than the size of a grain of wheat.  The terminations, both proximally and distally, of the elongated elliptical ganglionated trunk are obscurely united by ganglia or commissura, cords.
    A ganglion is composed of a larger or smaller number of multipolar nerve cells enclosed in a capsule of connective tissue.


    The bilateral symmetrical vertical ganglionated trunk of the sympathetic is connected to the spinal cord by means of the rami communicantes, which are two bands of nerves extending from the spinal nerves to the ganglia of the trunk of the sympathetic.    These central communicating branches are known as gray (sympathetic) and white (visceral) rami communicantes.  The ganglionated trunk of the sympathetic nerve emits important visceral branches from its different segments (cervical, dorsal, lumbar and sacral) to the viscera of the thoracic, abdominal and pelvic cavities.  The following table will present a bird's-eye view of the segments of the trunk of the sympathetic nerve with their important branches.


I.  Trunk of the cervical sympathetic.  (Truncus Sympathicus Cervicales).  Two to three.
    1. Superior cervical ganglion (ganglion cervicale superior).
    2.  Middle cervical ganglion (ganglion cervicale medium).
    3.  Inferior cervical ganglion (ganglion cervicale inferior).

II.  Trunk of the dorsal sympathetic. (Truncus Sympathicus Dorsalis).
    Ten to twelve.
    Emits splanchnic nerves.
    (Coeliac Plexus).

III.  Trunk of the lumbar sympathetic.  (Truncus Sympathicus Lumbalis).
    Four to five.
    Emits lumbar branches to plexus aorticus.

IV.  Trunk of the pelvic sympathetic. (Truncus Sympathicus Pelvinus).
    Four to five.
    Emits visceral nerves.


I.  Branches of the Cervical Trunk of the Sympathetic.

    The cervical sympathetic trunk is a projection proximalward (toward the cranium) along the great cervical vessels.
    The branches of the three cervical ganglia and commissural cord are distributed to structures of the head, neck and thorax and consist of:
    (a) Motor fibres to involuntary muscles (pupil dilators).
    (b) Vaso-motor fibres to head, neck and proximal limbs.
    (c) Pilo-motor fibres along cervical spinal nerves.
    (d) Cardiomotor fibres.
    (e) Secretory fibres.
    The trunk cervical ganglia are located on the prevertebral muscle dorsal to the carotid artery.  It extends from the first rib to the base of the skull.
    The cervical sympathetic trunk is characterized by the absence of the white rami communicantes.  The cervical ganglia, usually coalesced, from seven to three in number, are important on account of the emitting of the pharyngeal plexus and cardiac nerves.
    A.  Superior Cervical Ganglion (Ganglion Cervicale Superius).
    SYNONYMS: Supreme cervical ganglion (ganglion cervicale supremum); the great cervical ganglion (ganglion cervicale magnum); the fusiform cervical ganglion (ganglion cervicale fusiforme); the olive-shaped cervical ganglion (ganglion cervicale olive).
    The superior cervical ganglion, 3/4 of an inch in length is the largest of the sympathetic trunk ganglia.  It is located at the base of the skull between the internal jugular vein and internal carotid artery.  It is irregular in form, however, chiefly spindle-shaped.  The commissural cord connects it to the middle cervical ganglion.
    The main branches of the superior cervical ganglion are:

    Central communicating branches
        1. Gray rami communicantes (no white).
        2. Communicantes with cranial nerves.

    Peripheral branches of the distribution.
        3. Emits branches to pharynx.
        4. Emits superior cervical cardiac nerves.
        5. Branches, to vessels (controlling lumen).

    B.  Middle Cervical Ganglion (Ganglion Cervicale Medium).
    SYNONYMS: The thyroid ganglia (Ganglion Thyroideum).
    The middle cervical ganglion sends branches:
    1.  (Central Communicating Branches) gray rami communicantes (no white).
    2.  The subclavian loop (Ansa Vieusseni, French anatomist, 1641-1716) enclosing the           subclavian artery and joining the middle and inferior cervical ganglia.
    3.  Peripheral branches of distribution, the middle cervical cardiac nerve.
    4.  Branches to the thyroid body.

    C.  Inferior Cervical Ganglion (Ganglion Cervicale Inferius).
    SYNONYMS: The first thoracic ganglion (Ganglion Thoracicum primum); the vertebral ganglion (Ganglion Vertebrale); the stellate ganglion (Ganglion Stellatum).
    The inferior cervical ganglion is irregular in dimension, form, location and branches.  The inferior cervical nerve emits:
    1.  (Central Communicating Branches) gray rami communicantes (no white).
    2.  Subclavian loop.
    3.  Communications with larynx.
    4.  (Peripheral branches of distribution).  The inferior cervical cardiac nerve.
    5.  Branches to vessels
        (a) Vertebral plexus.
        (b) Subclavian plexus.
    The bilateral trunks of the cervical sympathetic are not directly united by transverse nerve strands.

II.  Branches of the thoracic or dorsal trunk of the Sympathetic.
    The dorsal or thoracic ganglia composing the dorsal or thoracic trunk of the sympathetic generally consists of eleven ganglia of varied form and dimension connected by commissural cords of marked dimension.  The important feature of the thoracic sympathetic trunk is that the distal five or six ganglia give origin to the three splanchnic or visceral nerves which richly supply the abdominal viscera.  The branches forming the ganglionated thoracic cord may be divided into two kinds (a) central branches connecting with other nerves; (b) peripheral branches distributed in a plexiform manner to the thoracic and abdominal viscera.  The significant feature of the thoracic trunk of the sympathetic is the presence of the white rami communicantes (visceral nerves).  The central communicating branches are (both) the white and gray rami communicantes.  The peripheral branches of distribution of the thoracic trunk arise both from the ganglia and the commissural cord.  The important distributing branches in the practice of medicine for the abdominal viscera are the three splanchnic nerves; the distal ends of the splanchnic nerves practically form the abdominal brain - the visceral ruler of the peritoneal organs.  The splanchnic nerves are the abdominal visceral nerves.  The following table presents a bird's eye view of the branches of the thoracic sympathetic trunk:

    Branches of the thoracic sympathetic trunk.
    1.  (Central communicating branches) white rami communicantes.
    2.  Gray rami communicantes.
    3.  (Peripheral branches of distriubtion). (Pulmonary from II, III, and IV ganglia) to form the pulmonary plexus.
    4.  Aortic (from proximal 5 ganglia) to suply aorta.
    5.  The three splanchnic nerves (from the distal 7 thoracic ganglia and commissural cords) to supply the abdominal viscera.

    A. The Great Splanchnic Nerve  (Nervus Splanchnicus Major)
    Arises from the thoracic trunk between the fifth and ninth ganglia.  By the coalescence of several irregular strands a nerve of marked dimension is formed which passes distalward in the dorsal mediastinum and perforating the crus of the diaphragm terminates as the principal mass of the abdominal brain (semilunar ganglion).  The great splanchnic ganglion (ganglion splanchnicum maxium) is found on the trunk of the great splanchnic nerve within the thoracic cavity.

    B. The Small Splanchnic Nerve (Nervus Splanchnicus Minor).
    The small splanchnic nerve arises from the trunk of the thoracic sympathetic in the region of the ninth and tenth ganglia.  It courses adjacent to the bodies of the distal thoracic vertebrae, perforates the crus of the diaphragm adjacent to or with the great splanchnic and terminates irregularly in the abdominal brain, (and occasionally in the so-called aortic-renal ganglion).

    C.  The Least Splanchnic Nerve (Nervus Splanchnicus Minimus - inferior or tertius).
    The least splanchnic nerve arises from the last thoracic ganglion in the sympathetic trunk (or from the small splanchnic).  It perforates the diaphragm and terminates in the plexus renalis.  The bilateral thoracic trunks of the sympathetic are not directly united by the transverse nerve strands similar to the lumbar and sacral trunks.

III.  Branches of the Lumbar Sympathetic Trunk.
    The lumbar trunk of the sympathetic consists usually of four ganglia joined by commissural cords.  It is continuous proximally with the thoracic and distally with the sacral trunk of the sympathetic.  The lumbar trunk is located on the bodies of the lumbar vertebrae internal to the origin of the psoas muscle and ventral to the lumbar vessels.  The lumbar ganglia are not always bilaterally symmetrical in dimension, location, distance from each other and form.  The ganglia are larger than those of the dorsal or sacral trunk.  The commissural cords of the lumbar sympathetic trunk are longer, stronger and more irregular in number than the dorsal or sacral.  The branches from the lumbar gangliated trunk consist of two sets, viz.:

    A.  Central Communicating Branches.
    1.  The first two or three lumbar spinal nerves possess visceral branches which form white rami communicantes joining the proximal lumbar ganglia or commissural cord.
    These white rami communicantes comprise vaso-motor fibres for the tractus genitalis and motor fibres for the uterus and bladder.
    2.  Gray Rami Communicantes which pass to the ventral primary divisions of the lumbar nerves.  The rami communicantes (white and gray) are irregular in length, dimension and location.

    B.  Peripheral Branches of Distribution from the lumbar ganglia and commissural cord arises and pass to the plexus aorticus and aorta.  The lumbar sympathetic trunk sends branches to the plexus ureteris.  The branches are irregular in length, dimension, number and location.  The bilateral sympathetic trunk is directly united by several transverse nerve strands, chiefly extending from ganglion on one side to that on the other.

IV.  Branches of the Sacral Sympathetic Trunk.
    The sacral trunk of the sympathetic is a continuation of the lumbar trunk.  It terminates in a plexiform coalescence over the coccyx with the trunk of the opposite side.  The distal termination of the sacral sympathetic trunks are known as the ganglion impar or coccygeal ganglion.  There are usually four ganglia which united by a commissural cord decrease in dimension from sacral promontory to coccyx.  The ganglia are generally not bilaterally symmetrical in location, dimension or equidistant from each other.  The usual location is on the ventral surfcae of the sacrum on the internal border of the sacral foramina.  The ganglia scralia vary in number, dimension, location and form.  The bilateral sacral sympathetic trunks are united directly by numerous transverse nerve cords which are arranged in a plexiform manner (which I have termed plexus intertrunci sacralis).  The middle sacral trunk of the sympathetics, like that of the cervical and distal lumbar receives no white rami communicantes from the spinal nerves.
    The visceral branches (Pelvic Splanchnic) of the II, III and IV sacral nerves join the pelvic plexus (pelvic brain) without being directly connected with the sacral sympathetic trunk.  These nerves, however, are to be considered homologous with the white rami communicantes of the thoracic and lumbar (abdominal splanchnics).
    The II, III and IV sacral nerves transmit to the tractus genitalis (uterus) tractus intestinalis (rectum) and tractus urinarius (bladder) motor and inhibitory nerves, and also vaso-dilator fibres for the tractus genitalis.
    The branches of the sacral sympathetic trunk are of two kinds, viz.:

A.  Central Communicating Branches.
    I.  Gray rami communicantes arise from the ganglia and join the ventral primary division of the sacral and coccygeal nerves.  There are no white rami communicantes.
B.  Peripheral Branches of Distribution are:
    1.  Visceral branches of limited dimension which arise mainly from the proximal ganglia of the trunk and commissural cord and pass medianward to join the interiliac plexus and pelvic brain as well as the three kinds of pelvic viscera and adjacent vessels.
    2.  Parietal branches limited in dimension which ramify on the ventral surface of the sacrum, especially in relation with the sacral artery, forming what I have termed the plexus intertrunci sacralis.
    The four segments of the trunk of the sympathetic nerve, cervical, dorsal, lumbar and sacral, differ according to location and environment.
    The white rami communicantes (visceral nerves abdominal splanchnics) stream from the dorsal and proximal lumbar ganglia.
    The visceral nerves of the pelvic sympathetic trunk (pelvic splanchnics) do not pass through the sacral ganglia but through the II, III and IV sacral nerves.
    The distributing branches of the pelvic sympathetic trunk are the least important of any segmental trunk.  The bilateral cervical and dorsal sympathetic trunks are practically not directly united by transverse nerve cords, the bilateral lumbar and pelvic trunks are united by numerous transverse nerve cords (and plexuses).
    The bilateral cervical sympathetic trunks are united by two localized prevertebral plexuses, the pharyngeal and cardiac.
    The bilateral dorsal sympathetic trunks are united by a single prevertebral colossal pelvus-abdominal brain.
    Ganglionic coalescence occurs chiefly in the cervical trunk.  The ganglia are the most irregular in the pelvic trunk, the largest in the cervical and lumbar trunks.
    The commissural cords are multiple supernumerary in the lumbar  and sacral trunks only.
    The cervical sympathetic trunk and pelvic brain are the only segments so far subject to surgical intervention (extirpation).
Fig. 6. The trunk of the vasomotor nerve here presented was dissected under alcohol with care as regards connexions and relations.  The ellipse formed by the two lateral trunks is evident.  The ellipse extends from the cranium to the coccyx.  The two nerve trunks are especially united at the cranium (cervical part) at the coeliac axis (abdominal part) and the distal end (pelvic part).  Between the two lateral trunks of the nervus vasomotoritis lies the plexus aorticus, thoracicus, cerebrum abdominale, plexus aorticus abdominalis, interiliac nerve disc, plexus interiliacus, cerebrum pelvicum.