三焦下 ，在于足大指之前，少阳之后，出于 中外廉，名曰委阳。足太阳络也，手少阳经也。
〔《铜人》〕云∶委阳，在足太阳之前，少阳之后，出于 中外廉两筋间，承扶下六寸，此足太阳之别络。
刺入七分，留五呼，灸三壮，屈身而得之。详《铜人》云∶委阳在承扶下六寸，以今经文考之，当云一尺六寸。
谨按经文论委阳，在足太阳之前，少阳之后，出于 中外廉。又按经文取合穴法，取委阳者屈伸而索之，
取阳陵泉者正竖膝与之齐，下至委阳之前取之，是知委者曲也。委中即两 之中央，委阳即曲 之阳分，约文之
尽处，两筋间是。推其分野，正当太阳少阳之间，内外廉之界，故曰太阳之前，少阳之后， 中外廉也。
其穴正在约文尽处，两筋之间，屈伸而得之，故取法曰屈伸索之也。只正膝与之齐，阳陵泉正对其
穴，故曰取阳陵泉者，下至委阳之前取之也。又考诸尺寸则承扶下至其穴，正得一尺六寸，故愚断然谓《甲乙》
脱去“一尺”二字，无疑也。
三焦者，足少阳太阳之所将，太阳之别也。上踝五寸，别入贯 肠，出于委阳，并太阳之正，入络膀胱，
The lower He-Sea point of the Sanjiao (Triple Burner) is located anterior to the big toe and posterior to the Shaoyang channel, emerging between the medial and lateral tendons of the lower leg. It is named Weiyang (BL39). It is the connecting vessel of the Foot-Taiyang Bladder Channel and the lower He-Sea point of the Hand-Shaoyang Sanjiao Channel.
According to *Tongren* (Illustrated Manual of Acupoints), Weiyang is located anterior to the Foot-Taiyang channel and posterior to the Shaoyang channel, emerging between the two tendons on the lateral aspect of the lower leg, six cun below Chengfu (BL36). This is the divergent vessel of the Foot-Taiyang Bladder Channel.
Needle insertion depth is 7 fen; retain the needle for five breaths; moxibustion consists of three cones. The point is accessed by flexing the body. Detailed examination of *Tongren* states that Weiyang is six cun below Chengfu; however, based on a textual analysis of this classic, it should be stated as sixteen cun.
Respectfully consulting the classic text regarding Weiyang: it is located anterior to the Foot-Taiyang channel and posterior to the Shaoyang channel, emerging between the medial and lateral tendons. Furthermore, according to the method for locating He-Sea points described in the classics: when locating Weiyang, one seeks it through flexion and extension of the limb; when locating Yanglingquan (GB34), one sits upright with the knee vertical and level with the point, seeking it forward from Weiyang. From this, we know that "Wei" (委) implies bending or flexion. Weizhong (BL40) is at the center of the popliteal crease; Weiyang is on the Yang (lateral/posterior) side of the flexed popliteal region, specifically at the end of the descriptive boundary, which is between the two tendons. Analyzing its anatomical territory, it lies precisely between the Taiyang and Shaoyang channels, at the boundary of the medial and lateral aspects, hence described as anterior to Taiyang and posterior to Shaoyang, i.e., between the medial and lateral tendons. The point is exactly at the end of the popliteal crease, between the two tendons, accessible through flexion and extension; thus, the retrieval method is described as "seek through flexion and extension." If sitting upright with the knee vertical, Yanglingquan aligns directly with this point; therefore, the instruction "locate Yanglingquan... seek forward to Weiyang" refers to this alignment. Further dimensional verification confirms that the distance from Chengfu to this point is exactly one chi and six cun. Therefore, I firmly conclude that the *Jia Yi Jing* (Systematic Classic of Acupuncture and Moxibustion) omitted the characters "one chi," without doubt.
The Sanjiao channel is governed by the Foot-Shaoyang Gallbladder Channel and the Foot-Taiyang Bladder Channel; it is a divergent branch of the Foot-Taiyang Bladder Channel. Five cun above the malleolus, it branches off, passes through the intestines, emerges at Weiyang (BL39), runs parallel with the main trunk of the Foot-Taiyang Bladder Channel, enters and connects with the Bladder.