Transversalis fascia is a thin layer of fascia lining the transversus abdominis muscle. It lies between the transversus abdominis and the extraperitoneal fascia.
It is important to understand that the transversalis fascia, the diaphragmatic fascia, the iliacus fascia, and the pelvic fascia form one continuous lining to the abdominal and pelvic cavities. They are named customarily according to the structures they are associated with.
The femoral sheath in the lower limbs is formed from this fascia, in addition to fascia iliaca (the fascia covering the iliacus muscle.
Borders and attachments of transversalis fascia:
- Posterior aspect: Towards the posterior aspect, the transversalis fascia is lost in the fat covering the posterior surfaces of the kidneys.
- Inferior aspect: Inferiorly, the transversalis fascia is attached to the iliac crest in its entire length and posterior margin of inguinal ligament.
- Medial to femoral vessels: In this region, the fascia is thin and attached to the pubis and pectineal line. It descends in front of the femoral vessels to form the anterior wall of femoral sheath.
- Beneath the inguinal ligament: In this region, it is strengthened by a band of fibrous tissue that loosely connects to the inguinal ligament and forms the iliopubic tract.
Opening in the transversalis fascia (Deep inguinal ring):
The transversalis fascia has an oval opening near the midpoint of the inguinal ligament. This opening is known as deep inguinal ring. It transmits the spermatic cord (in males) or round ligament of uterus (in females).
The opening in the fascia is not visible externally. It is very hard to locate during dissection of a cadaver. The reason is that transversalis fascia is prolonged on the structures passing through the opening as the internal spermatic fascia. Internally there is a well established passage but externally on can see nothing.