The femoral sheath (crural sheath) is formed by a prolongation downward, behind the inguinal ligament, of the fasciæ which line the abdomen, the transversalis fascia being continued down in front of the femoral vessels and the iliac fascia behind them.
The sheath assumes the form of a short funnel, the wide end of which is directed upward, while the lower, narrow end fuses with the fascial investment of the vessels, about 4 cm. below the inguinal ligament.
It is strengthened in front by a band termed the deep crural arch. The lateral wall of the sheath is vertical and is perforated by the lumboinguinal nerve; the medial wall is directed obliquely downward and lateralward, and is pierced by the great saphenous vein and by some lymphatic vessels.
The sheath is divided by two vertical partitions which stretch between its anterior and posterior walls. The lateral compartment contains the femoral artery, and the intermediate the femoral vein, while the medial and smallest compartment is named the femoral canal, and contains some lymphatic vessels and a lymph gland imbedded in a small amount of areolar tissue. The femoral canal is conical and measures about 1.25 cm. in length.
Its base, directed upward and named the femoral ring, is oval in form, its long diameter being directed transversely and measuring about 1.25 cm.
The femoral ring is bounded in front by the inguinal ligament, behind by the Pectineus covered by the pectineal fascia, medially by the crescentic base of the lacunar ligament, and laterally by the fibrous septum on the medial side of the femoral vein. The spermatic cord in the male and the round ligament of the uterus in the female lie immediately above the anterior margin of the ring, while the inferior epigastric vessels are close to its upper and lateral angle.
The femoral ring is closed by a somewhat condensed portion of the extraperitoneal fatty tissue, named the septum femorale (crural septum), the abdominal surface of which supports a small lymph gland and is covered by the parietal layer of the peritoneum. The septum femorale is pierced by numerous lymphatic vessels passing from the deep inguinal to the external iliac lymph glands, and the parietal peritoneum immediately above it presents a slight depression named the femoral fossa.