tains a layer of longitudinal fibers. At the lower end all the longitudinal fibers are intimately interlaced with certain other muscles that are attached to the rectum-the levator ani muscle, the external sphincter ani muscle, and the internal sphincter ani muscle-and can be followed down through them to the skin (Fig. 86).

The external sphincter ani muscle (Figs. 87, 13) is an elliptic layer of striped muscular fibers which surround the anal opening and lie directly under the skin. Behind it is fastened with a tendon to the tip of the coccyx; in front it blends with the transversus perinei and sphincter vaginæ muscles. It is the true voluntary sphincter by which fæces and gases are kept back.

The internal sphincter ani muscle is only a thicker part of the circular layer of the rectum situated inside of the external sphincter, and consists of unstriped muscle-fibres, with a considerable admixture of striped fibers. It gets fibers from the deep layer of the deep perineal fascia, from the superficial transversus perinei, and from the bulbocavernosus muscles. It surrounds the anal canal, and is an inch high. It contracts and relaxes by reflex action, and is not subject to the will.

The levator ani muscle (Figs, 87, 14, 15) forms an important part of the pelvic floor, and will be considered under that heading.

The mucous membrane shows numerous folds. In the lower part of the rectum these have a longitudinal direction, and are called the columns of Morgagni, and the depressions between them are called the sinuses of Morgagni. In the upper part transverse folds preponderate. Three of these (more rarely only two or one), situated within reach of the examining finger, are particularly developed, and called Houston's valves. Commonly one of them is placed on the anterior wall, about 2 inches above the anus; the others an inch higher up, on the posterior wall. They are semicircular, and, the transverse muscles extending from one to the other (Fig. 88), they form together a kind of circular valve, which ordinarily lies below the accumulated feces. This apparatus has been described as a third sphincter, but is, according to Chadwick, a detrusor; that is, it serves to expel the feces.1

The mucous membrane is covered with columnar epithelium and has many glandular pouches. The transition from the skin to the mucous membrane is distinctly marked by a so-called white line.

Relations.-The rectum lies in contact outside with the left ureter and left internal iliac artery. It has the left ovary in front, and rests on the pyriformis muscle and the sacral plexus. It is bound to the sacrum by the mesorectum in the upper part, and by fibrous connective tissue and fat lower down. It lies in the gap left between the

J. R. Chadwick, "The Functions of the Anal Sphincters, so-called, and the Act of Defecation," Trans. Am. Gyn. Soc., ii. pp. 43-56. I have, however, frequently palpated these folds on patients, and do not find that it causes any expulsive effort.

sacro-uterine ligaments. Loops of the small intestine lie between its upper part and the uterus, unless the latter be pushed far back by an overfilled bladder. In the narrow lower part of Douglas's pouch there are, as a rule, no intestines; the rectum hugs the cervix and lies close up to the vagina. The anal canal forms the posterior wall

Rectum cut open longitudinally, and the mucous membrane dissected off, so as to show the circular muscular fibres (Chadwick): DD', anterior and posterior segment of the superior detrusor fæcium (or third sphincter); S, inferior detrusor fæcium (or internal sphincter); A, anus; † and correspond to the same points in Fig. 85. This drawing shows the mus cular fibres passing from the anterior to the posterior segment of the superior detrusor, by the action of which they may be approximated to each other.

of the perineal body, which separates it from the entrance to the vagina and the vulva.

Vessels and Nerves.-The rectum has an abundant blood-supply. The arteries are the superior hemorrhoidal from the inferior mesenteric, the middle hemorrhoidal from the internal iliac or one of its branches, a branch of the middle sacral, and the inferior hemorrhoidal

from the internal pudic. The veins form a rich plexus, and lead the blood through the inferior and middle hemorrhoidal to the internal iliac, and through the superior hemorrhoidal to the superior mesenteric, a branch of the vena porta. The lymphatics go to the sacral

Pelvic Peritoneum with Empty Bladder; mesial section of frozen body, (Fürst). The dotted line indicates the peritoneum; a, rectum; b, vagina; c, bladder; d, uterus; e, below pouch of Douglas; f, symphysis pubis.

glands. The nerves come partly from the sympathetic nerve (the hypogastric plexus), partly from the cerebro-spinal system (sacral plexus).

Function.-The rectum is a receptacle for the feces, and expels

them by the combined action of its circular and longitudinal fibers, the first contracting above and relaxing below the mass to be removed, and the latter preventing sacculation, straightening the canal, and pulling the relaxed part of the intestine up over the fecal mass. The internal sphincter can, by its contraction, push the mucous membrane out through the anus, and thus becomes an expulsive muscle, as is very apparent in the horse. The mucous membrane is capable of absorbing, which explains many bad effects of constipation, and is utilized for the administration of drugs and artificial alimentation.

THE PELVIC PERITONEUM.

The pelvic peritoneum is a continuation of the abdominal peritoneum, and covers the organs in the pelvis more or less completely.

FIG. 90.

Diagram designed to show the antero-posterior outline of the pelvic peritoneum in the mesial pelvic plane, with distended bladder (Ranney): PP, peritoneum; R, rectum; U, uterus; B, bladder; S, symphysis pubis. The vesico-abdominal, the vesico-uterine, and Douglas's pouch are made very apparent.

It has been likened to a cloth which is being lifted up by pushing the organs from below up under it, by which they themselves acquire a covering and certain folds and pouches are formed. Thus the reader may imagine that the peritoneum is represented by a sheet of thin muslin, and that an apple representing the bladder, a pear representing the uterus, and a banana representing the rectum are placed under

it. Beginning in front, the peritoneum passes from the anterior abdominal wall at the upper end of the symphysis pubis over on the top of the bladder (Fig. 89), covers its posterior wall down to the level of the internal os of the uterus, and its sides behind the obliterated hypogastric artery. When the bladder is much distended it rises up into the abdominal cavity, and the peritoneum forms a pouch between the abdominal wall and the bladder (the vesico-abdominal pouch), the deepest point of which lies an inch above the symphysis (Fig. 90).

From the posterior surface of the bladder the peritoneum passes over on the anterior wall of the uterus, covering it entirely above the cervix, and leaving a pouch between the two called the vesico-uterine pouch. When the bladder is over-distended, the bottom of this pouch is raised a little, as represented in the figure. Next, the peritoneum covers the whole posterior surface of the uterus, and goes even generally an inch down behind the posterior wall of the vagina, and passes then over on the rectum, leaving a pouch between the two called Douglas's pouch or the recto-uterine pouch. This pouch varies very much in depth, sometimes ending at the posterior utero-vaginal junction, and in other cases extending down as far as the entrance of the vagina. Next, the peritoneum covers the anterior surface of the middle portion of the rectum, surrounds the whole upper portion of the same, and passes over on the sacrum as the meso

rectum.

From the sides of the uterus the peritoneum passes out to the wall of the pelvis, forming the broad ligaments, which cover the Fallopian tubes, the round ligaments, the ovarian ligaments, and the attached border of the ovaries.

The uterus and the broad ligaments together form a partition which divides the pelvic cavity into an anterior inferior and a posterior superior part (Fig. 52, p. 55). The anterior compartment as a whole is called the utero-abdominal pouch. In it we notice the utero-vesical ligaments and the round ligaments of the uterus. It is filled by the bladder, and, when this is empty, by loops of the small intestine. Its lateral parts, where the entrance is to the obturator canal, have been designated as the obturator pouch, or paravesical pouch (Fig. 91, II). When the bladder is moderately filled, the loops of the small intestine are found in the upper part of the utero-vesical pouch.

The posterior compartment may be subdivided into a central deep part-i. e. Douglas's pouch-and two shallower lateral parts called para-uterine pouches (Fig. 91, I). The bottom of the latter has been designated particularly as the retro-ovarian shelves (Polk). The boundary-line between these three parts is the sacro-uterine ligaments. On the side wall of the para-uterine pouch is seen the ureter running under the peritoneum (Fig. 53, p. 56). The ovaries project into