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


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    Extending from the abdominal brain (the coeliac axis) to the pelvic brain (cervico-uterine junction) there exist two rich and mighty nerve plexuses, plexus aorticus and plexus interiliacus.
    For convenience of description and significance in practice I will divide this plexus into two grand divisions, viz.:
    (a)  The plexus aorticus extending from the coeliac axis to the aortic bifurcation;  (b)  the plexus hypogastricus or more significantly plexus interiliacus, which extends from the bifurcation of the aorta (sacral promontory) to the junction of uterus and vagina.  The plexus interiliacus is important because it is the great highway of travel for afferent (initiative or spontaneous) and efferent (reflex peripheral) genital nerve forces.  I shall view the plexus interiliacus as originally belonging and accompanying the common iliac vessels.  However, by erect attitude, distalward movements of the tractus genitalis and increasing dimensions (especially lateralward) to the pelvis, coalescence of the proximal extremities of the two branches of the plexus interiliacus arose.  That is, the original nerve plexuses accompanying the common iliac arteries gradually moved medianward from them.  Hence the term plexus interiliacus is particularly appropriate.  The plexus interiliacus has experienced a variety of names during the past two centuries.
    Synonyms: Superior hypogastric plexus (plexus hypogastricus superior, Tiedemann, 1822).  Medial hypogastric plexus (plexus hypogastricus medius).  Impar (odd, single, impaired) hypogastric plexus (plexus hypogastric impar).  Interiliacal plexus (plexus interiliacus, Waldeyer, living).  The great uterine plexus (plexus uterinus magnus, Tiedemann, 1822).  Pelvic plexus (plexus pelvicus, Thomas Snow Beck, 1845, 1814, 1847).  The hypogastric ganglion, i. e., layer (lamina gangliosa hypogastrica, Gabriel Gustave Valentine, German anatomist, 1810-1883).  The common uterine plexus (plexus uterinus communis, Tiedemann, 1822).  Iliac plexus (plexus illacus-anatomica nomina, Basel).  Distal part of the aortic plexus (plexus aorticus distal, Henle-Fred Gustav Jacob Henle, German anatomist, 1809-1885).
    The plexus interiliacus I shall consider under three distinct headlines, viz.: (a) interiliacal nerve disc (proximal end); (b) trunk of the plexus interiliacus (central segment); (c) pelvic brain (distal end or ganglion cervicale).


    The proximal end of the plexus interiliacus, which I shall term the interiliacal nerve disc of the sacral promontory, is practically a plexus of nerve cords compressed or flattened dorso-ventrally.  The interiliacal disc is the result of coalescence of the distal end of the plexus aorticus, located at the aortic bifurcation, practically on the sacral promontory and the distalward movements of the tractus genitalis producing traction and extension on the nerve disc of the sacral promontory.  The interiliac nerve disc is practically a plexiform nerve mass located at the proximal end of the plexus interiliacus.  The arrangement of the interiliacal disc consists in the coalescence on the same promontory of the afferent nerve-plexus aorticus and branches from the distal bilateral lumbar ganglia - and the emission of efferent nerves: (a) two bilateral large plexuses to the pelvic brain; (b) branches to the tractus intestinalis (rectum hoemorrhoidal); (c) branches to the tractus genitalis (uterus, vagina, oviduct); (d) branches to the tractus urinarius (ureter, bladder).


    II.  Holotopy (relation to general body).  The interiliac nerve disc is located on the median line in the space between the major bifurcation and the distal end of the abdominal end cavity immediately proximal to the lesser pelvis.  It is a coalesced unpaired organ situated extraperitoneally on the sacral promontory, dorsal to the peritoneum.  It is strongly ensconced in connective tissue at the most accessible portion of the abdomen for palpation.
    II.  Skeletopy (relation to osseous system).  The interiliac nerve disc lies on the ventral surface of the distal lumbar and proximal sacral vertebrae.  It lies practically on the brain of the inner osscous pelvis.
    III.  Syntopy (relation to adjacent viscera).  The interiliac nerve disc, coalesced (unpaired), is located centrally in the space between the major aortic bifurcations which practically includes the ventral surface of the two distal lumbar and two proximal sacral vertebrae.  It is securely ensconced in strong dorsal subperitoneal connective tissue.  It is situated between the peritoneum and pelvic fascia.  The interiliac nerve disc is limited to the space between the coalescence of the plexus aorticus (aortic bifurcation) and the emission or divergence of the plexus interiliacus (second sacral vertebrae).  The interiliac nerve disc lies dorsal to certain changeable mobile loops of the enteron and mesenteron and possess variable relations to the sigmoid and mesosigmoid.  In peritonotomy, in spare subjects, the interiliac nerve disc may be observed shimmering whitish through the dorsal peritoneum.
    IV. Idiotopy (relation of the component segments).  The interiliac nerve disc consists of a nerve plexus compressed, flattened, dorso-ventrally, and interspersed with fenestra of varying number and dimension.  The fenestra increase in number and dimension from proximal to distal borders. Dimensions:  The interiliacal disc is some two inches in length and three fourths of an inch in width. Form.  The form is that of truncated cone.  The lateral borders are bounded by nerve cords.  The proximal border fuses with the plexus aorticus.  The distal border coalesces with the emerging efferent lateral interiliacal plexuses.


    It consists of a flattened, band-like nerve plexus in a sheath of firm, dense, connective tissue, located in the interval between the two common iliac arteries.  It is formed by a continuation of the plexus aorticus plus prolongations from the ganglia lumbales.  It is a flat plexiform nerve mass at the junction of the distal lumbar and proximal sacral vertebrae.  I have termed it the interiliac nerve disc, as it contains no constant distinct ganglia.  Some authors claim it contains no ganglia, while others claim it contains some ganglia, the latter being the more probable.  The interiliac disc is significant as it emits (efferent nerves) from its distal border, the two nerve plexuses which rule the pelvic viscera.   The interiliac nerve disc is an example of the principle elsewhere noted that at every emission of a major (visceral) artery from the abdominal aorta there exists a ganglion (or nerve disc).  Practically there should be two ganglia at the aortic bifurcation.  However, coalescence occurred and one ganglion or disc resulted - the interiliac nerve disc (or ganglion).  Efferent nerve branches from the interiliac disc not only accompany the two common iliac, ovarian, superior haemmorhoidal and sacral arteries but emit the two great interiliac plexuses (for the pelvic viscera) as well as branches to the ureters, left colon and sigmoid.  The interiliac nerve disc is important in practice because it is practically accessible to manipulation, massage.  By gentle irritation or massage of the interiliac disc in post partum hemorrhage the plexus interiliacus will be stimulated, which, supplying the uterus, will induce the elastic and muscular bundles of the myometrium to act like living ligatures, limiting the uterine vessels, and checking haemorrhage.  It is not the supposed constriction of the aorta that checks the haemorrhage.


    The trunk or central segment of the interiliac plexus (paired) extends from the interiliac nerve disc to the pelvic brain.  The plexus interiliacus consists not merely of nerve strands, for it is composed of nerve plexuses the commissures and cords of which are band or ribbon-like in character surrounding apertures or fenestra of various dimensions which increase in area toward the distal end.  The plexus interiliacus increases in breadth from proximal to distal end, i. e., from interiliac nerve disc to pelvic brain.  The proximal end is relatively small and composed of a few nerve cords, the distal end is broad and divides into numerous branches.  The course of the interiliac plexus is proximally along the internal side of the pelvic vessels while distally it courses along the dorsal and rectal wall with which it is intimately connected by connective tissue and, when it again resumes intimate association with the pelvic vessels the length of the trunk of the plexus interiliacus averages some 3 ½ inches.  Numerous nerve branches from the V lumbar ganglion and from the I, II, III and IV sacral ganglia join the external border of the plexus interillacus.  From the internal border of the plexus interiliacus numerous branches pass to the rectum, ureter, uterus, vagina, bladder.  From the plexus pass numerous nerves to the pelvic vessels.  The trunk of the plexus interiliacus is profoundly associated with the rectal wall, sharing in its movements or contraction of and dilatation.  The intimate and profound connections of the trunk of the plexus interiliacus with the rectal wall explains the favorable therapeutic value of the rectal enema due to stimulation of the plexus.  The rectum is practically surrounded, ensheathed by two great bilateral interiliac plexuses, i. e., the rectum lies in the boot-jack angle produced by the divergence of the plexuses.  The plexus interiliacus possesses a remarkable anatomic feature, which is that it sends some two strong nerves directly to the uterus without first passing through the pelvic brain (demonstrated with very extraordinary facility in infant cadavers).


    The broad distal end of the plexus interiliacus, a plexiform fenestrated nerve mass, unites with the branches of the II, III and IV sacral nerves to form the pelvic brain (ganglion cervicale).  The resulting union of the distal end of the plexus interiliacus and sacral nerves - a plexiform ganglionated mass, the pelvic brain - rules the physiology of the pelvic viscera, especially the vascularity of the genitals.  The pelvic brain is elsewhere described in detail.


    The plexus interiliacus, like the plexus aorticus, is one of the great and important nerve plexuses of the abdomen.  It practically supplies the tractus genitalis; distal end of tractus intestinalis (rectal, sigmoid) ; and distal end of tractus urinarius (ureter, bladder).  The plexus interillacus is double, bilateral, presenting practically no anastomosis.  It is accessible to manipulation through the abdominal wall as well as per rectum and per vaginam.  Dilatation of the rectum produces its favorable therapeutic effects through the plexus interiliacus by flushing the capillaries and stimulating visceral function, especially respiration.  The plexus interiliacus is the dominating plexus of the pelvis.  It is the great assembling nerve center of the pelvic organs and is solidly and compactly bound and anastomosed to all other pelvic sympathetic nerves as well as the I, II, III and IV sacral spinal nerves.  The following table presents an idea of the vast extent and richness of distribution of the branches of the plexus interiliacus.  It should be remembered that the vast majority of the branches of the plexus interiliacus first pass through the pelvic brain before supplying the pelvic viscera (especially those to the tractus genitalis).

1.  Tractus Intestinalis (haemorrhoidal)
    a. colon (left)
    b. sigmoid
    c. rectum

2. Tractus Genitalis
    ligamentum latum
    pelvic subserosium

3. Tractus Urinarius

4.  Tractus Vascularis
    arterial plexuses accompanying
    all pelvic arteries

5.  Tractus lymphaticus
    (all pelvic lymphatic glands are richly supplied),

    A peculiar character of the plexus interiliacus is that it is considerably disassociated from arterial vessels - unlike the plexus aorticus.  The pelvic visceral plexus or branches of the plexus interiliacus possess similar features.  On the contrary, the visceral plexuses or branches of the abdominal brain notably accompanying the visceral arteries.


    The plexus interiliacus experiences an age relation according to the sexual phases as presented by the utero-ovarian artery in: (a) pueritas, (childhood), a quiescent, undeveloped state with limited blood, ganglion cells and neurilemma; (b) pubertas, a developmental state (of congestion) of multiplication of ganglion cells and increased neurilemma; (c) menstrual phase, a functional state of engorgement (of the vaso uterina), which further increases the neurilemma if not the ganglion cells; (c) gestation, a state of complete development of the tractus genitalis (continuous maximum engorgement of the utero-ovarian artery) with the multiplication of ganglion cells and periganglionic tissue with neurilemma; (d) puerperium.  The elastic and muscular bundle of the myometrium having contracted like living ligatures, the enormous volume of blood passing through the utero-ovarian artery is checked, maximum engorgement suddenly ceases, the ganglion cells perhaps remain the same in number, however, decreasing in dimension; while the periganglionic tissue, the neurilemma and associated connective tissue decrease, degenerate; (e) climacterium. This phase of sexual life represents beginning atrophy from lessening of blood volume in the utero-ovarian artery.  The ganglion cells diminish in size and number as well as the periganglionic tissue, while the associated connective tissue multiply; (f), senescence.  This is the atrophic sexual phase - death of parenchymatous and increase of connective tissue framework of viscera.  The muscularis and elastic fibres of the myometrium and oviduct decrease while the connective tissue increases.  The wall of the utero-ovarian artery increases in thickness while the lumen decreases in dimension.  The ganglion cells of the plexus interiliacus decrease in number and dimension while the ganglion cell, nucleus and body cell outlines become less distinct.
    The periganglionic connective tissue and neurilemma decrease while the associated connective multiplies.  In senescence the plexus interiliacus, which was originally destined for the tractus genitalis, gradually fades from its maximum dignity of structure and function.  Senescence has returned the plexus interiliacus to its primitive phase of pueritas or quiescent existence.


    It is accessible to manipulation from proximal to distal end through the abdomen, per rectum or per vaginam.  Massaging or stimulating the plexus interiliacus induces the muscular and elastic bundles of the organ which it supplies to contract by controlling the blood volume.  The most typical example for the employment of therapeutics on the plexus interiliacus is during postpartum haemorrhage.  It is the irritation, massage of the plexus interiliacus, that induces muscular and elastic bundles of the myometrium to contract and consequently control the hemorrhages.  It is not the obstruction produced in the aorta by the pressure, the technique of which is almost impossible, for the two ovarian arteries would still continue to force large volumes of blood to the uterus.  Light abdominal stroking, digital manipulation of the uterus in postpartum hoemorrhage irritates, massages the plexus interiliacus and its branches, which induce the elastic and muscular bundles of the uterus to contract like living ligatures on the blood vessels, checking haemorrhage.  The so-called uterine inertia of long, tedious labor may be due to paresis of the plexus interiliacus from trauma by the child's head.  Sudden cessation of parturient peristalsis - arrest of labor - is doubtless due to trauma by the child's head on the plexus interiliacus, a sudden paresis.  Vaginal or rectal injections (hot or medicated) stimulate the plexus interiliacus, hastening labor.  Electricity will accomplish similar effects.  The flat, band-like form of the plexus interiliacus protects it from trauma during parturition.  Massage of the plexus interiliacus will end all alleviating constipation by stimulating active peristalsis and secretion of the left colon, sigmoid and rectum.  The plexus interiliacus may be stimulated by means of hot fluid or food taken, in the stomach.  The irritation passes from the stomach over the plexus gastricus to the abdominal brain, whence it is reorganized and emitted over the plexus interiliacus, inducing more vigorous uterine contractions.  By appropriate systematic massage of the plexus interiliacus stimulation of the pelvic viscera may be effected, resulting in a vigorous circulation.

Fig. 9 This illustration presents the sympathetic nerves following the arteries.  I dissected this specimen (man 40) with care, and the artist, Mr. Klopper, sketched exactly from the model. 1 and 2, abdominal brain.  Pn, Pneumogastric nerve; sp.  Nervus Splanchnicus major.  Ad, adrenal; Dg, ganglion diaphragmaticum; Adn, 10 adrenal nerves (right), (left), 7. G. R. arteria renalis (right and left partially duplicate).  N. Ganglia renalia (left).  Ur, ureteral nerves.  S. G. and 5 upper ganglia spermatica. 1, ganglion mesentericum inferior; X, ganglionic coalescence of nerves at the vasa spermatica and ureteral crossing. 5 ganglionic coalescence of the nerves at the crossing of the ureter and vasa iliaca communism IB, Plexus interiliacus (hypogastricus) surrounding the rectum.  ID is the fenestrated nerve disc of the sacral promontory.  V, Vena cava emitting the vena ovarica on which is ensheathed the plexus ovaricus.


Fig. 10.  This specimen I dissected with care under alcohol.  The plexus interiliacus extends from the discus interiliacus (D) to the pelvic brain (A).  Observe: (1) Two nerve strands are emitted from the interiliac plexus to the uterus previous to passing through the pelvic brain (A). (2) Note the contribution of the lateral sacral chain of ganglia and II and III sacral nerves to the plexus interitiacus. 3) Bear in mind the intimate relation of the plexus interiliacus to the rectum proximalward and distalward.

Fig. 11.  I dissected this specimen in 1894 from a spare subject having enormously large vasomotor nerves.  The aorta divided into the iliacs at the junction of the III and IV lumbar vertebrae. 112, genital ganglion; 173, third lumbar ganglion (R) ; 114, genito-rectal ganglion; 103, lumbar lateral chain of ganglia; 173, third lumbar nerve ; 90, lumbar nerve; 91, lumbar nerve; 179, fourth lumbar ganglion (R) 104, lateral chain of ganglia; 181, com. iliac artery arising in this case at third lumbar vertebra; 188, inferior renal ganglia; 174, fourth lumbar nerve (.R); 189, fifth lumbar ganglion (R); 93, lumbar nerves; 114, genital ganglion; 115, hypogastric plexus; 134, first sacral ganglion (L) ; 179, fourth lumbar ganglion (R); 116 hypogastric plexus; 125, lumbo-sacral cord; 135, first sacral ganglion (R) ; 136, genital ganglion; 118, hypogastric plexus; 126, first sacral nerve (L);  170, lumbar sacral cord; 130, first sacral nerve (R) ; 158, right sacral plexus; 137, second sacral ganglion; 117, hypogastric plexus; 156, rectum; 127, second sacral nerve (L).  From author's life-size chart on the sympathetic nerve.

Fig. 12.  This specimen I dissected under alcohol.  D, interiliac nerve disc.  Interiliac iliac nerve disc (D) to the pelvic brain (A).  Observe: (1) that two large nerve stands are emitted from the interiliac plexus to the uterus without first passing through the pelvic brain. (2) The plexus interiliacus is intimately associated with the rectum.  (3) The lateral sacral chain of ganglia and sacral nerves contributes branches to the interliliac plexus. 
     The II, III, IV and V sacral nerves contribute to form the pelvic brain, while in some specimens the I sacral nerve contributes a branch or branches.