**Core Concept**
The superficial inguinal ring is a small, oval opening in the aponeurosis of the external oblique muscle, allowing for the passage of structures between the superficial and deep fascia. It is a significant anatomical landmark in the inguinal region.

**Why the Correct Answer is Right**
In females, the superficial inguinal ring transmits the round ligament of the uterus, which is a fibromuscular cord that extends from the uterus to the labia majora. The round ligament plays a crucial role in supporting the uterus and maintaining its position within the pelvic cavity. The superficial inguinal ring is the only passage through which the round ligament exits the inguinal canal, allowing it to traverse the superficial fascia and reach its destination in the labia majora.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the superficial inguinal ring does not transmit the deep inguinal lymphatic vessels, which are actually found in the deep fascia and communicate with the lymph nodes of the abdominal wall.

**Option B:** This option is incorrect because the superficial inguinal ring does not transmit the spermatic cord in females, as the spermatic cord is a male structure that contains the vas deferens, testicular vessels, and testicular nerves.

**Option C:** This option is incorrect because the superficial inguinal ring does not transmit the ilioinguinal nerve, which is a nerve that innervates the skin of the inner thigh and the inguinal region.

**Clinical Pearl / High-Yield Fact**
The superficial inguinal ring is an important anatomical landmark in the inguinal region, and its identification is crucial in surgical procedures such as hernia repair. The round ligament of the uterus, which passes through the superficial inguinal ring, can be used as a landmark for identifying the inguinal canal and the location of the ring.

**Correct Answer: D. Round ligament of the uterus.**