Cervix

The cervix or uterine cervix is the lower constricted segment of the uterus. Owing to its relationships, it is less freely movable than the uterine body, so that the latter may bend on it. The long axis of the cervix is therefore seldom in the same straight line as the long axis of the uterine body. 

Gross anatomy

The cervix is somewhat conical in shape, with its truncated apex directed downward and backward, but is slightly wider in the middle than either above or below.

The canal of the cervix is somewhat fusiform, flattened from front to back and broader in the middle than at either extremity. It communicates through the internal orifice with the cavity of the body, and through the external orifice with the vaginal cavity. The wall of the canal presents an anterior and a posterior longitudinal ridge, from each of which proceed a number of small oblique columns, the palmate folds, giving the appearance of branches from the stem of a tree; to this arrangement the name arbor vitæ uterina is applied. The folds on the two walls are not exactly opposed, but fit between one another so as to close the cervical canal. 

Attachments

Musculotendinous and ligamentous

• anterior: pubocervical ligament
• lateral: transverse cervical ligaments (Cardinal or Mackendrodt's) - attached to the side of the cervix uteri and to the vault and lateral fornix of the vagina
• posterior: uterosacral ligaments
• inferior: puborectalis and pubovaginalis parts of the levator ani muscle

Relations 

The cervix projects through the anterior wall of the vagina, which divides it into an upper, supravaginal portion, and a lower, vaginal portion.

Supravaginal portion

• anterior: separated from the bladder by fibrous tissue (parametrium), which extends also on to its sides and lateralwardlateral wall between the layers of the broad ligaments.
• lateral: the uterine arteries reach the margins of the cervix within the broad ligaments, while on either side the ureter runs downward and forward in it at a distance of about 2 cm from the cervix.
• posterior: the supravaginal cervix is covered by peritoneum, which is prolonged below on to the posterior vaginal wall, when it is reflected on to the rectum, forming the rectouterine excavation. It is in relation with the rectum, from which it may be separated by coils of small intestine. 

Vaginal portion

The vaginal of the cervix projects free into the anterior wall of the vagina between the anterior and posterior fornices. On its rounded extremity is a small, depressed external orifice of the uterus, through which the cavity of the cervix communicates with that of the vagina. The external orifice is bounded by two lips, an anterior and a posterior, of which the anterior is the shorter and thicker, although, on account of the slope of the cervix, it projects lower than the posterior. Normally, both lips are in contact with the posterior vaginal wall.

Histology

In the cervix, the mucous membrane is sharply differentiated from that of the uterine cavity. It is thrown into numerous oblique ridges, which diverge from an anterior and posterior longitudinal raphé. In the upper two-thirds of the canal, the mucous membrane is provided with numerous deep glandular follicles, which secrete a clear viscid alkaline mucus; and, in addition, extending through the whole length of the canal is a variable number of little cysts, presumably follicles which have become occluded and distended with retained secretion, the ovula Nabothi. The mucous membrane covering the lower half of the cervical canal presents numerous papillæ. The epithelium of the upper two-thirds is cylindrical and ciliated, but below this it loses its cilia, and gradually changes to stratified squamous epithelium close to the external orifice. On the vaginal surface of the cervix the epithelium is similar to that lining the vagina, viz., stratified squamous.