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ANATOMY OF^ ANAL CANAL^ AND^ RECTUM
THE SURGICAL ANATOMY OF^ THE^ ANAL^ CANAL
AND RECTUM.
By C. NAUNTON MORGAN,^ M.B.,^ F.R.C.S. (Senior Assistant^ Surgeon,^ St.^ Mark's^ Hospital,^ etc.)
EMBRYOLOGY.
In the early embryo the^ allantois,^ which lies in the body stalk, is situated at
the hind end of^ the foetus and^ is at first^ meirely^ a^ continuation^ of^ the^ hind^ gut.^ As
growth proceeds, the^ hind^ end of the^ embryo^ assumes^ a^ curvature^ and^ the^ allan- tois and body^ stalk^ are^ displaced^ ventrally.^ The^ differentiation^ of^ the^ allantois and hind gut is now easy to see and the sharp bend between^ the^ two^ becomes dilated to form the^ cloaca.
During the backward growth of the embryo, its dorsal^ portion^ grows^ more^ quickly than the ventral so that there is now a^ portion^ of gut lying^ behind^ the^ junction of the allantois and hind gut. This is^ known^ as the^ post-allantoic^ gut.^ The^ hind gut and post-allantoic gut soon^ become^ shut^ off from^ the^ allantoic^ portion^ of the cloaca by the uro-rectal septum which^ grows^ down^ from^ the^ junction of^ the allantois and the hind gut;^ thus the^ uro-genital^ passages^ are^ separated from^ the alimentary tract.
On the ventral aspect of the post-allantoic gut, a thickening in^ the^ epiblast appears, which breaks down forming a depression called the^ proctodeum.^ It^ will be noted therefore that the proctodeal membrane invaginates the^ ventral^ aspect of the post-allantoic gut. This proctodeal membrane finally breaks^ down^ and its remnants represent in the adult, the free edges of the valves^ of^ Morgagni.^ Since the proctodeal membrane invaginates the post-allantoic gut^ on^ its^ ventral^ aspect, the sinuses of Morgagni must be deeper and^ more^ prominent^ on^ the^ posterior aspect of the anal canal. This is exactly what^ is^ found in^ the^ adult, and thus^ there appears to be no doubt that these^ valves^ mark the site^ of^ junction^ between^ the post-allantoic gut and the^ proctodeum.
The junction of the allantois with^ the^ hind^ gut is situated^ at^ the^ posterior^ limit of the body cavity: this point, in the fully developed individual, being the^ reflec- tion of the peritoneum off the anterior^ wall of the^ rectum^ on^ to^ the bladder^ or
vagina. The peritoneal reflection^ therefore,^ is the^ dividing^ line between the hind
gut and the post-allantoic gut, and the^ sub-peritoneal portion^ of the^ rectum^ repre-
sents the post-allantoic gut of^ the^ embryo.
The commonest site for termination of the abnormal rectum is at the^ junction
of the hind gut with the^ post-allantoic gut.
From the study of development, the^ rectum^ and anal canal^ are^ divisible into three parts:--
(a) The^ Pelvic^ Rectum^ or^ Hind^ Gut^ Portion.^ This is the^ portion^ of^ the rectum situated^ above^ the^ peritoneal^ reflection between the first and third
valves of Houston. It has^ no^ mesentery, no^ appendices epiploica, and
the taenia begin to^ form^ a^ uniform muscle^ coat,^ and the^ superior^ haemorr-
hoidal artery divides^ into^ branches^ which^ run^ on^ to^ the^ gut^ along^ the
lines of the (^) peritoneal reflection.
August, 1936 287
(b) The^ Perineal^ Rectum^ or Post-Allantoic^ Portion.^ This^ forms^ the^ ampulla
of the rectum and the constricted^ portion^ of^ the anal^ canal above the
anal valves. Branches of the^ superior^ haemorrhoidal artery approach^ the
anterior surface at the peritoneal reflection and pierce^ the wall of^ this
portion of the gut.
(c) The^ Proctodeum.^ This^ is^ the portion^ of^ the^ anus below^ the^ anal^ valves.
Malformations of^ the^ Rectum.
Malformations of^ the^ rectum^ have^ been^ lucidly explained^ by^ Keith in terms^ of comparative anatomy. The cloaca in the amphibian receives both the^ urinary and genital ducts and the^ termination^ of the^ rectum.^ In^ man,^ the^ cloaca^ is represented by the^ trigone of^ the^ bladder^ and^ a^ portion^ of^ the^ urethra.^ Very occasionally, the rectum ends abnormally in^ the^ trigone^ and^ this^ represents^ the amphibian form. In^ the^ turtle,^ a^ stage^ further^ is^ reached,^ the^ rectum ending in^ the^ cloaca^ nearer^ the tail^ of^ the embryo^ than^ the^ uro-genital^ ducts.
The human rectum sometimes ends in the^ prostatic urethra^ just distal^ to^ the veramontanum. This type corresponds^ to^ the normal^ state^ of^ affairs in the^ turtle. Termination of the^ rectum as^ a^ fibrous cord^ at^ the base of the^ prostate^ represents a stage of arrest between the^ amphibian and^ the tortoise.^ In^ the further course^ of
evolution, the anus^ migrates from its^ intra-cloacal^ position^ to^ an^ extra-cloacal^ one
in the^ perineum.^ The various^ types^ of^ malformation^ represent^ various^ stages^ of
development.
There are three main^ groups of^ malformations:-
(x) Persistence^ of^ the^ Original^ Communication^ with^ the^ Cloaca.
A. In the male. (a) The^ commonest^ opening (in^ this^ group)^ is in the urethra
at the lower end of^ the^ veramontanum,^ i.e.,^ distal to the^ uro-genital
openings. When this^ occurs, the^ opening is^ too^ small^ to^ allow faeces^ to
pass through and it is said^ that^ a^ sphincter^ muscle is^ present.
(b) The^ opening^ may^ be^ very^ rarely^ in^ the^ trigone^ of the bladder.^ Fig.^ I.
[Plate I.]
(c) The^ opening^ may^ be^ at^ the^ internal^ meatus. (d) The opening may be^ at^ the^ apex^ of the^ prostate.
(e) The^ opening^ is^ occasionally^ on^ the under^ surface^ of^ the^ penis^ at^ the^ fraenum or at the scrotal raphe. The^ anus^ in^ this^ type^ is^ extra-cloacal^ but is
drawn forwards by the^ developing^ penis.
B. In the female. (^) (a) The commonest^ opening^ occurs^ in^ the vulva^ in^ the fossa navicularis. This corresponds to^ the^ commonest^ abnormality^ in the male. The writer^ has^ noticed^ in^ some^ cases^ that^ there appears^ to be a sphincter muscle round the termination of^ the^ rectum^ and,^ there-
fore, when operating for repair of this^ defect,^ it is wise^ to^ transplant^ not
only the termination of^ the^ rectum^ but^ some^ of the tissue around^ it, including the vaginal wall at the orifice.
288 POST-GRADUATE MEDICAL JOURNAL August, 1936
(x) The External Sphincter. The external^ sphincter^ of the anus is a^ trilaminar
muscle, the three portions of which correspond^ in^ development^ to^ the three layers of the abdominal wall which, like the^ external^ sphincter, is derived from the primitive ventral muscle.
The three portions of the external sphincter^ are:- (a) The subcutaneous external sphincter. (b) The superficial external sphincter. (c) The deep external sphincter.
(a) The Subcutaneous External Sphincter^ is an^ annular^ muscle^ encircling^ the lowest part of the anal canal.^ Not^ only^ can^ this muscle^ be^ felt^ as^ a distinct band, but it can^ also^ be^ seen lying^ under^ the skin at the^ anal orifice. It^ has no^ bony^ attachments,^ and^ its^ fibres^ decussate^ both anteriorly and posteriorly.
In front, a few fibres pass to the back of the scrotum forming a^ rudi- mentary retractor scroti. In the female, the subcutaneous^ external sphincter is usually well developed and anteriorly its fibres^ blend^ with^ the sphincter vaginae.
This muscle lies immediately below the internal^ sphincter^ and^ is mainly in the same plane but lying slightly^ external.^ Its^ upper edge^ is separated from the lower edge of the^ internal^ sphincter by^ a distinct depression just inside the^ anal verge.^ This depression^ has been^ called the anal inter-muscular septum.^ This^ portion^ of^ the external^ sphincter is quite mobile^ underneath^ the skin^ and may^ be^ easily^ pushed^ outwards with a^ finger. Fig.^ 7. During^ contraction^ it^ will^ be^ seen^ to^ move inwards and its relation therefore to the lower edge of the^ internal^ sphincter may vary^ considerably.^ It^ may even overlap^ the^ lower^ edge^ of^ the internal sphincter externally.
(b) The^ Superficial^ External^ Sphincter.^ This^ portion^ of^ the^ muscle^ is elliptical and lies immediately above and external^ to^ the^ preceding^ portion of the muscle. It is attached posteriorly to^ the^ coccyx and^ may^ be^ called
the coccygeal portion of the^ external^ sphincter.^ It arises^ by^ aponeurotic
and muscular fibres from^ the^ dorsal^ aspect^ of the^ coccyx^ and also^ from the ano-coccygeal raphe. The^ muscle^ passes^ forwards from^ its^ insertion in two^ halves^ on^ either side^ of the^ anal^ canal.^ Anteriorly,^ it is^ inserted into the central^ point^ of^ the^ perineum^ but some^ fibres^ pass^ to^ the^ skin and others outwards to the tuber ischii. The^ muscle^ is^ narrower anteriorly and posteriorly, being broadest at^ the sides of^ the^ anal canal.
(c) The Deep External^ Sphincter.^ The^ deepest^ portion^ of^ the^ muscle^ lies
immediately above and slightly external^ to^ the^ superficial^ portion.^ Like the subcutaneous external sphincter, it^ is^ annular^ and^ has^ no^ attachment to the^ coccyx.^ Its^ upper^ border is^ intimately^ attached,^ in^ the^ posterior half of its circumference, to the^ outer^ and inferior^ aspect^ of the^ pubo- rectalis. It cannot^ be^ separated from^ this^ muscle.^ In the^ anterior^ por-
tion of^ its circumference^ its^ upper^ edge lies^ quite^ free but some^ of^ its
fibres decussate to gain attachment to^ the^ ischium, forming^ the^ transverse perinei muscles. These^ bony attachments^ help^ to^ steady^ the muscle during its action.^ Figs.^ 2,^3 and^ II^ [Plate^ 2].
290 POST-GRADUATE MEDICAL JOURNAL August, 1936
Auut 96 AAOYO NLCNLADRCU 9
FIG. 2.
Diagrammatic representation of the portions of external sphincter ani. Note:--the vertical levels of the various parts cannot be shown.
.:._:.. :'.^ [.
LEELOFAORMAL "RING--- -
'EXTSPHM-.^ '^ 3uS.
EXT. (^) SPH. SUPERFICIALIS
EXT. m ...u...wc
iE. !,^ S^ ia.: ,^ oz-wa EXT. 5PH. SUEFCAIUS
- (^) -. (^) ·Z. ':"'-... ; "-
PaWTERWA IMMORM40AL RPLS ..m?^ OF^ PBO-
tu COAT" SEPT·'
.:.L.-.. (^) .: ...:
.: -^ .. :
FIG. 3.
Diagram of^ sagittal section^ of^ anal^ canal,^ shewing^ relationship^ of external^ sphincter, internal sphincter, pubo-rectalis, Longitudinal^ muscle,^ hemorrhoidal^ plexuses^ and lining of anal canal.
(2) The^ Pubo-rectalis^ Muscle.^ This^ portion^ of the levator^ ani muscles^ has^ an important r6le^ in^ the control^ of^ continence.^ It^ forms^ a^ sling^ round^ the termination of the^ rectum^ and its^ junction^ with the anal canal.^ It^ arises in front from the lowest portion of the^ symphysis pubis^ and^ the^ adjacent
part of the pubis and also^ from^ the^ deep^ layer^ of^ the^ triangular^ ligament.
From this^ origin, its^ passes downwards and backwards^ on^ either side of the prostate (^) (or vagina) and^ rectum.^ The^ fibres^ of^ either^ side^ are
August, 1936 ANATOMY^ OF ANAL CANAL^ AND^ RECTUM^291
a
canal. It passes downwards^ from^ the^ level^ of^ the^ ano-rectal^ ring,
enveloping the^ internal sphincter^ and^ lying between^ it and the deep^ and
superficial portions^ of^ the^ external sphincter^ externally.^ Between the
lower border of the internal sphincter and the^ upper border^ of the^ sub-
cutaneous external sphincter,^ it is^ firmly attached^ to the^ lining^ of^ the anal canal. Its attachment is broad and^ somewhat^ fan-shaped.^ The
lining of the anal canal is^ held down^ tightly^ by^ this^ insertion^ and^ the
depression called^ the^ anal^ inter-muscular^ septum^ is^ produced.^ Most fistulae enter the anal canal at this inter-muscular^ insertion^ of^ the^ longi- tudinal muscle. Some^ of^ the^ fibres^ of the^ longitudinal^ muscle pass outwards between the deep and superficial portions, between^ the^ super- ficial and subcutaneous portions and^ also^ between^ the^ subcutaneous portion and the^ skin^ at^ the^ anal^ verge,^ ending^ in the^ ischio-rectal^ fossa or peri-anal subcutaneous fat. Spread of^ infection^ from^ the anal^ canal probably occurs along these^ inter-muscular^ planes.^ The^ insertion^ of^ the
longitudinal muscle holds in^ place^ non-prolapsing^ internal^ haemorrhoids.
As internal hemorrhoids increase in size and^ prolapse through^ the^ anus,
the longitudinal muscle^ is^ elongated^ but^ its^ insertion remains intact.^ This
explains the^ presence of^ a^ distinct sulcus in^ cases of^ intero-external haemorrhoids. The sulcus is much^ more^ pronounced^ in^ thrombosed^ pro- lapsed piles. In^ the modified Salmon^ operation^ for internal^ hemorrhoids,
these longitudinal^ fibres^ are^ divided,^ so^ exposing^ the^ sub-mucous^ layer.
Figs. 3, 5, and 6.
B -.^ A
C-... D
FIG. 5. FIG. 6.
Relationships and terminal^ attachments of longitudinal muscles^ of^ anal^ canal. [E. T. C. (^) Milligan].
A. Subcutaneous external^ sphincter. B. Intermuscular septum. C. Lower border of^ internal^ sphincter. D. Longitudinal muscle. E. Prolapsed thrombosed^ intero-external^ pile.
Relationships of^ longitudinal muscle of anal canal^ to^ haemorrhoids^ and sphincters. [E.^ T.^ C.^ Milligan].
A. B. C. D. E.
Subcutaneous external^ sphincter. Submucosa with vessels. Internal sphincter. Longitudinal muscle^ cut^ and^ retracted. Prolapsed pile.
August, 1936 ANATOMY OF^ ANAL CANAL^ AND RECTUM^293
::,., ... -j
294 POST-GRADUATE MEDICAL
(4) The Internal^ Sphincter.^ The internal sphincter^ is a^ continuation^ of the circular muscle coat of the rectum which becomes markedly thickened. It commences just above. the level of the ano-rectal ring and is tubular, completely encircling almost the whole length of the^ anal canal.^ It^ extends downwards almost to the lower end of the anal canal and at its lower edge is just above the level of the anal inter-muscular^ depression.^ It does not end in the upper part of the anal canal as described in most textbooks of anatomy. Figs. 3, 5, 6, 7, and II. [Plate (^) 2].
;:'::::~ .: -:.'-.".:' ..
- l l FIG. 7.
- I- .....· Showing lower^ border^ of^ internal sphincter. Subcutaneous^ sphincter ani externus retracted outwards
The Nerve Supply of the^ internal sphincter is by means of the sympathetic and para-sympathetic systems. Its action is similar to that of the circular muscle coat of the colon and rectum. By its relaxation^ and contraction^ it helps to push faeces through the anal canal. Its action differs considerably from that of the external sphincter which, together with the pubo-rectalis, enables the^ act of de- faecation to be controlled by the will under normal circumstances. There must exist, therefore, a very nice co-ordination between these two distinct types of muscle and it is suggested that^ derangements^ in^ this^ balance produce hypertrophy^ and possibly fibrous degeneration of the internal sphincter. From the study of more
than forty dissections of the muscles of^ this region by Pallares,^ we^ have^ noticed
that the^ size^ of the internal^ sphincter^ varies very^ considerably,^ being^ especially
large in the aged and in cases which have suffered from^ prolonged constipation.
By pushing outwards the subcutaneous external^ sphincter and incising the
lining of the anal^ canal, the^ lower^ edge of^ the^ internal^ sphincter^ is^ seen^ presenting
a white glistening appearance. Occasionally it^ can^ be^ felt^ tightly contracted, under an anesthetic. The upper part of a fissure-in-ano lies^ over^ the lower^ end of the internal sphincter and^ also^ across^ the^ annular^ subcutaneous^ external sphincter. This latter muscle is in^ spasm in such^ cases^ and its division is^ a necessary part of the^ operation^ for^ cure^ of^ a^ chronic^ fissure.^ Fibrosis also
occurs in the subcutaneous sphincter and^ its^ division^ produces relaxation of the
anus and relief of^ symptoms.
From the foregoing description of^ the^ anal^ musculature, it^ is^ possible to
palpate with precision certain^ landmarks.
294 POST-GRADUATE MEDICAL JOURNAL August, 1936
POST-GRADUATE MEDICAL JOURNAL
The Anal Inter-Muscular Septum.
The formation of this depression has^ already^ been described.^ It lies^ just
inside the anal verge and if the finger be placed at the depression,^ the lower^ edge
of the internal sphincter^ is^ palpated^ immediately^ above and the^ subcutaneous sphincter below and externally. Fig. IO.
:.. n..ul ...S.
.,.. :.....'Zq
.....
FIG. 10. Palpation of^ intermuscular^ septum. Middle of distal (^) phalanx at level of anus. I.S. Intermuscular (^) Septum.
The Lining of the Anal Canal. Prom the^ study^ of^ sections^ prepared^ by^ Dr.^ Cuthbert^ Dukes^ at^ St.^ Mark's Hospital, the following^ description^ has^ been^ obtained.^ Just above the^ level^ of the ano-rectal ring, where the circular muscle coat of the bowel^ commences^ to become thicker to form the internal sphincter, the columnar epithelium^ of^ the rectum becomes thinner and so also^ does^ the^ muscularis mucosm.^ The^ columnar glandular epithelium continues downwards^ over^ the ano-rectal^ ring^ into^ the upper part of the anal canal for about half^ an^ inch^ or^ slightly^ less.^ It^ is^ dull red^ in colour. Below^ this, the columnar^ epithelium^ changes^ gradually^ to^ cuboid epithe- lium of several layers thickness. This type of epithelium extends^ down^ over^ the columns of Morgagni to the level of the anal^ valves,^ becoming^ thinner^ as^ it descends. The columns of Morgagni are formed by^ vessels^ running^ longitudin- ally in the mucosa, the mucous membrane being^ thrown^ into folds.^ The^ colour of this cuboid lining is still red^ but^ much^ paler than^ the dull^ red^ of^ the^ columnar mucous membrane.
The valves of Morgagni are^ situated^ about^ three-quarters^ of^ an^ inch below the level of the^ ano-rectal^ ring.^ The^ epithelium^ changes^ abruptly^ to^ modified squamous or^ a^ transitional^ type of^ epithelium^ at^ the level of the valves and^ just above this point the muscularis mucose^ disappears. This^ type of^ epithelium covers the lowest portion of^ the internal^ sphincter and is^ more^ firmly adherent^ to the subjacent tissues than^ the cuboid and columnar^ epithelium^ above.^ Immedi-
ately below the^ insertion of^ the^ longitudinal^ muscle of the^ rectum^ it becomes
gradually more^ definitely^ squamous.^ Its^ extent^ is about^ three-eighths^ of an inch
and its colour distinct, being pale and^ slightly bluish.
296 August, 1936
ANATOMY OF ANAL CANAL AND RECTUM
Below the anal inter-muscular septumn, true skin is encountered and cutaneous
glandular elements are present.^ It is^ at this^ site that^ Hilton's^ white line^ occurs,
but this much described line is only rarely seen.^ The line of the valves,^ however,
can readily be seen through^ a^ proctoscope. The^ subcutaneous external^ sphincter
is covered by true skin on its anal as well as its inferior aspect.. Fig. 3.
The position of the internal and external haemorrhoidal plexuses^ and the con-
necting vessels lying in the columns^ of^ Morgagni are seen^ in^ the diagram.^ In-
ternal haemorrhoids are due to dilatation of^ the radicles of^ the^ superior^ hemorrhoid
vein lying in the internal haemorrhoidal plexus^ and^ external^ hemorrhoids are^ due
to dilatation of the external haemorrhoidal plexus which lies superficial to^ the^ sub-
cutaneous external sphincter. When^ the connecting^ vessels^ lying in^ the^ columns
of Morgagni become dilated, an^ intero-external^ hemorrhoid is^ produced. The valves and sinuses of^ Morgagni^ are^ more^ numerous and prominent^ on the posterior wall^ of^ the^ anal^ canal, as already^ stated.^ Lying^ under^ the^ epithelium^ in this region and also extending outwards into the substance of the internal sphincter are glandular structures described by Johnson, Dukes and others,^ named^ intra- muscular glands. These glands may open into^ the^ columns^ but^ more^ commonly into the sinuses of Morgagni. They are of two types,^ simple tubular,^ ending^ in the sub-mucosa and branched glands ending in the underlying muscles.^ Gordon- Watson has described several cases, in which there seems to be^ no^ doubt^ that^ a
fistula-in-ano originated in these glandular structures.^ Tucker^ and^ Hellwig,^ in^ an
investigation into the condition^ of^ cryptitis,^ have^ noted^ that^ the^ mucosa^ of^ thie
sinuses of Morgagni^ are not as^ a^ rule^ the site of^ infection but that^ the^ infection
commences in these intramuscular glands. The mucous membrane^ above^ the^ level^ of^ the^ valves is^ either^ insensitive^ to
pain or^ its sensation^ is^ markedly^ diminished.^ On^ the^ other^ hand, the^ epithelium
at this level and below it, is highly sensitive, more so than^ the^ true skin.^ It^ is
supplied by^ branches^ from^ the^ inferior^ haemorrhoidal^ nerve.^ It^ has^ been^ pointed
out by Pennington that about 85 per cent. of all^ proctological diseases occur^ in this region. THE RECTUM.
The rectum commences^ opposite the^ third^ piece^ of the^ sacrum^ and^ ends^ at^ a
point z-in. in front^ and^ I-in.^ below^ the^ tip^ of^ the^ coccyx^ at^ the^ level of^ the^ apex
of the prostate. It^ is^ about^ 5-in.^ in^ length^ and^ follows the^ sacral^ curve.^ In
addition, there^ are^ two^ important^ lateral^ flexures-one^ convex^ to the^ right^ opposite
to the junction of the 3rd and 4th pieces of the^ sacrum^ and another to^ the
left at the level of the sacro-coccygeal articulation.^ These^ curves^ must^ be^ remem-
bered when passing a sigmoidoscope. The^ mucous^ membrane is^ loosely^ attached
to the muscle coat, especially in^ children,^ so^ favouring prolapse.^ Contraction of
the bowel throws the^ mucous^ membrane^ into^ folds which^ disappear^ when the rectum is distended with air. The (^) perineal portion of^ the^ rectum^ is dilated^ to
form the ampulla which, in^ a^ normal state, is^ empty.
There are two^ constant^ transverse^ folds of^ mucous^ membrane^ and^ muscle seen in the^ rectum, namely^ the^ valves^ of Houston.^ The^ proximal valve is situated
on the^ right side^ at^ the^ junction^ of the^ sigmoid^ colon and^ pelvic^ rectum.^ The
other, which may be called^ the^ main^ valve of^ Houston, is situated at the level of the peritoneal reflection^ (the junction of the hind^ gut and^ post-allantoic^ gut) on the anterior^ aspect of^ the^ bowel.^ Two other folds^ may^ be^ present,^ one^ in the
pelvic rectum^ on^ the^ left^ side^ and^ the other in the^ perineal^ rectum^ on^ the left
posterior aspect I-in. above^ the^ anal canal.
August, 1936 297
The Blood Vessels of the Rectum.
The superior hemorrhoidal artery is a continuation of the inferior mesenteric
and lies behind the rectum. It divides into two branches at the level of the third
piece of the sacrum and these branches pass on to the lateral aspects of the rectum following the reflection of the peritoneum.
The site and mode of division of this vessel has been studied from X-ray
photographs of injected specimens and it has been found to be extremely variable,
so much so that no accurate anatomical description is possible. About (^) 4-in. above the anus, the main branches further divide and pierce the muscle coat, running down in the sub-mucous layer as straight regularly spaced vessels to end as a series of (^) loops at the level of the internal sphincter.^ The^ superior^ hemorrhoidal supplies the mucosa of the rectum and the musculature of its upper portion. It
has been^ stated^ by Miles^ that the right main branch of the artery^ divides^ into two
further branches, a right anterior and right posterior. The left main branch does not divide. These three arteries mark the position of the three primary piles. The right (^) posterior branch and the left main branch further divide into two terminal branches indicating the site of the secondary piles. Very occasionally the left main branch again divides giving rise to an additional secondary pile anteriorly. The middle hemorrhoidal artery lies, as already stated, in the lateral liga-
ments and supplies mainly the muscle coat of the upper part of the rectum. The
inferior hemorrhoidal arteries supply the anal canal.
The Veins.
The venous return from the rectum is by means of the superior, middle and inferior hemorrhoidal veins. The main veins follow the same course as the artenries.
The external hemorrhoidal plexus, around^ the^ anal^ canal, drains^ mainly into
the inferior haemorrhoidal veins but also^ communicates^ with^ the^ middle^ and
superior hemorrhoidal^ veins^ through^ the^ internal^ hemorrhoidal^ plexus.
The superior hemorrhoidal vein is formed by the^ junction of about^ six vessels of considerable (^) size which (^) run upwards in the sub-mucosa of the rectum for three to
five inches, being more^ or less parallel to one another and devoid^ of^ valves.^ They
then pass through the muscle coats of the bowel and join to form, as a^ rule, a
single venous^ trunk.
Since these tributaries of the superior haemorrhoidal vein are large and run
in the sub-mucosa, carcinoma cells, as they extend^ through the^ rectal^ wall, may
easily erode a venous channel in this situation at^ a^ comparatively early stage and
give rise to hepatic metastases. This may occur^ with^ quite a^ small^ carcinoma, especially when^ placed on^ the^ posterior wall and^ when^ it^ is^ "button-like."
It has been further noted that during the extra-rectal spread of carcinoma,
growth extends along the (^) peri-vascular lymphatics; the carcinoma spreading upwards around the walls of the vessels. Malignant cells^ may conceivably pass
into the^ venous^ stream^ from^ the^ extra-rectal^ growth, especially in^ the^ region of the
recto-sigmoid junction.
The Lymphatics.
The lymphatics of the^ anal^ canal below^ the^ level^ of^ the^ valves^ of^ Morgagni
pass to^ the^ Inguinal Lymph^ Nodes.
August, 1936 ANATOMY^ OF^ ANAL CANAL^ AND^ RECTUM^299
300 POST-GRADUATE MEDICAL JOURNAL August, 1936
The lymphatics of the rectum above this level are divisible into intramural and extra-mural. The intra-mural lymphatic vessels communicate with^ the lymph sinus which lies between the rectal wall and the surrounding fat. It is imperative therefore to remove with the rectum, all the fat between it and the sacrum. The extra-mural lymphatics extend in the ischio-rectal fossa to the internal^ iliac^ glands, along the upper surface of the levators to the internal iliac glands and posteriorly to the glands behind the rectum. They also extend upwards along the superior hemorrhoidal vessels to the pelvic meso-colon and to glands at the bifurcation of the left common iliac artery. Spread of growth along all these zones is pos- sible, but very careful dissection and histological investigation of 250 specimens of carcinoma of the rectum at St. Mark's Hospital shows that spread into the retro-rectal lymphatic glands and upwards along the main vessels, is by far the most constant. Extension into the ischio-rectal fossa or along the levators is^ very uncommon and only occurs in advanced inoperable growths where the^ main upward lymphatic channel has been^ blocked. In^ only seven^ cases^ was^ there evidence of downward spread and^ it^ was^ noted^ that^ these^ occurred^ only^ in very
advanced cases with extensive permeation of the peri-vascular lymphatics. It is
also very unusual to find involvment of the para-colic glands secondary to a
carcinoma of the rectum. In this series only one case showed these glands to be involved.
I am indebted to Dr. Vicente Pallares who is my Clinical Assistant at^ St.
Mark's Hospital, for his help in^ verifying, by extensive^ dissection, the^ arrangement
of the muscles in^ this region, and^ to^ H.^ Bussey, B.Sc., for the^ preparation of
diagrams etc.
REFERENCES: Dukes,^ Milligan, Cuthbert,^ E.T.C.^ and Personal^ Morgan, communioation.^ C.N.,^ "Surgical^ Anatomy of^ the^ Anal^ Canal,"^ Lancet,^ 1934,^ ii,^ 1,150^ &^ 1,213. Gordon-Watson, C. and Dodd, H., "Observations on Fistula in Ano," Brit. Jour. Surg., 1935, xxii, 703. Abel, A. Lawrence, "The Pecten; The Pecten Band; Pectenosis and Pectenotomy," Lancet, 1932, i, 714. Thompson, Peter, (^) Myology of the Pelvic Floor, London. 1899. McGregor, A. Lee, (^) Synopsis of Surgical Anatomy, Bristol, 1932. Miles, W. E., "The Pathology of Spread of Oancer of^ the^ Rectum," Surg. Gyn.^ &^ Obst.,^ 1931, liit, 350. Tucker, C. C. and Hellwig, C. A.,^ "Histopathology^ of^ Anal^ Crypts,"^ Surg. Gyn.^ &^ Obst.,^ 1934, lviii,^ 145. Johnson, F. P., "The Development^ of the^ Rectum," Amer.^ Jour.^ Anat.,^ 1914,^ xvi,^ 1.
Mr. C. Naunton (^) Morgan
PLATE 2.
Anatomy of Anal.Canal and Rectum
Pubo-rectalis - fibres.
The two deeper portions of ext. sphincter fused together.
Extension of longit. muscle between por- tions of ext. sphincter.
Subcutaneous external sphincter
Longit. muscle of rectum at level of ano-rectal ring.
-- Internal sphincter.
-- Longit. muscle.
I Termination (^) of longit. muscle.
FIG. 11. Microphotograph demonstrating musculature of anal canal^ (Pallaris)
