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(Colloquially referred to as the coccyx, it is the location of the Changqiang (Long Strong) acupoint, also known as Juegu (Stub Bone), and further called Qionggu (Exhausted Bone).) This area is the intersection of the Foot-Taiyang Bladder Meridian and the Du Mai (Governing Vessel). (*Ling Shu* states: The collateral branch of the Du Mai is named Changqiang; it runs alongside the spine to the nape, scattering over the head. It also states: In cases of internal obstruction leading to urinary retention, needle the Foot-Shaoyin and Foot-Taiyang meridians, using a long needle on upper points.)

It also belongs to the Foot-Shaoyin Kidney Meridian. (*Mingtang Jing* states: The Changqiang acupoint is located in the depression below the end of the sacrum/coccyx at the tip of the spine; it is the collateral branch of the Du Mai and the site where the Qi of the Foot-Shaoyin condenses. Shen Chengzhi says: The tip of the spine is the convergence point of the Foot-Shaoyin Kidney Meridian and the Foot-Shaoyang Gallbladder Meridian.)

(This refers to the buttocks; the sacral bone is called the Ba Liao (Eight Holes) bone. On both sides of the sacral bone, there are four bony foramina each, named Shangliao (Upper Hole), Ciliao (Secondary Hole), Zhongliao (Middle Hole), and Xialiao (Lower Hole); with eight acupoints on each side, left and right, hence the name Ba Liao bone.) This area is the intersection of the Foot-Taiyang Bladder Meridian, the Du Mai (Governing Vessel), and the Chong Mai (Penetrating Vessel). (*Ling Shu* states: Ying Qi combines with the Foot-Taiyang meridian and follows the spine down to the sacrum. It also states: A branch of the Foot-Taiyang meridian descends from the middle of the waist, flanking the spine, passing through the buttocks, and entering the popliteal fossa. Diseases generated by this meridian include pain in the lower back, sacrum, popliteal fossa, calf, and foot. *Su Wen* states: The collateral of the Du Mai winds around the buttocks and joins with the Middle Collateral of the Foot-Shaoyin and the Great Yang [Foot-Taiyang]. It also states: Regarding the swelling and pain in the lower back mentioned by the Taiyang channel, the commentary notes: Bi refers to the flesh of the buttocks. Shen Chengzhi says: The human body has the concept of one valley and eight streams. The large gathering of muscle is called a valley; the one valley refers to the buttocks. The small gathering of muscle is called a stream; the eight streams refer to the two elbows, two knees, and four wrists. Between the streams and valleys, Ying and Wei Qi circulate, and Da Qi gathers. Therefore, the collateral of the Du Mai winds around the buttocks; the Chong Mai is the Sea of Blood, primarily responsible for irrigating and moistening the streams and valleys. Gu Yingbai says: The text's mention of "large gatherings of muscle" refers generally to the meridians. Since there are twelve primary meridians, there are also twelve large valleys. There are 365 Sun Luo (Sun Collaterals); excluding the main acupoints of the twelve meridians, there are 353 small streams, not just one valley and eight streams. Moreover, the classics do not contain the term "one valley," so it is unclear on what basis Shen Chengzhi makes this claim.) It also pertains to the Foot-Taiyin Spleen Meridian. (*Su Wen* states: When pathogenic factors invade the collateral of the Foot-Taiyin meridian, it causes lower back pain that radiates to the lower abdomen and controls the thigh region, making supine breathing difficult. One should needle the gap between the waist and sacrum. Commentary notes: The collateral of the Foot-Taiyin meridian merges with the Yangming meridian from the thigh, passes upward through the center of the sacral bone, and knots with the Jueyin and Shaoyang meridians at the lower liao points, then enters the abdomen along the inner aspect of the sacral bone. Thus, lower back pain radiates to the lower abdomen and controls the middle of the thigh; the gap between the lumbar and sacral bones is called the "Jie" (gap/solution).) It also belongs to the Foot-Shaoyin Kidney Meridian and the Foot-Shaoyang Gallbladder Meridian. (*Ling Shu* states: If the kidney descends, it causes lower back and sacral pain, making flexion and extension impossible, termed Hu Shan (Fox Hernia). If the kidney is tilted, it causes severe lower back and sacral pain. It also states: The sinews of the Foot-Shaoyang meridian knot anteriorly at the Futu acupoint and posteriorly at the sacrum. Its pathology involves tendon tightness, pulling the posterior thigh and subsequently drawing into the sacrum.)