Author: Yin Hongchun
3.1 Definition of the Tongue Midline
The tongue midline is originally an anatomical term. It refers to the line drawn longitudinally from the tip to the root along the center of the tongue’s dorsal surface (see Figure 3-1). A normal tongue midline should lie exactly in the middle between the left and right halves, remaining straight, free from lateral deviation, bulging, vertical curvature, cracks, or breaks. Any deviation of the tongue midline from its central position — whether leaning sideways, undulating (concavities and convexities), tilting, laterally bulging, cracking, or breaking — carries pathological significance in both Traditional Chinese Medicine and Western medicine.
When drawing the tongue midline, the following points should be considered: First, pay attention to the naturally occurring textures on the tongue, including grooves, cracks, depressions, and elevations. Special attention should be given to the most depressed and most elevated points at the tip and root of the tongue, as these two points often mark the beginning and end of the tongue midline. Second, assess whether the rise and fall of qi on the left and right sides of the tongue truly deviates to the degree indicated by the midline you have drawn. If there is no obvious left-right deviation of qi, then the false midline suggested by those grooves, depressions, or elevations should be discarded, and the midline position should be determined based on the central line between the left and right halves of the tongue. Changes in the tongue midline are one of the most important and objectively reliable bases for diagnosing disorders in the ascent and descent of the body’s qi.
The rules for interpreting tongue midline deviations are as follows:
3.1.1 Rightward deviation of the midline: The midline shifts toward the right side of the tongue (Figure 3-2), resulting in a larger left side and a smaller right side. This indicates left excess and right deficiency, specifically liver excess and lung deficiency, presenting an image of Liver Wood insulting Lung Metal. At the same time, excess Wood overacts on Earth, leading to Spleen Earth deficiency and weakness. Liver excess manifests as stagnant liver qi, with patients prone to suppressed anger and experiencing distending discomfort in the rib-side region. Liver depression restraining the spleen often leads to spleen deficiency symptoms, such as poor appetite, abdominal distension, diarrhea, or weak bowel movements. Lung deficiency manifests as cough, shortness of breath, and an inability to inhale fully. This essentially corresponds to the “excess in the East, deficiency in the West” concept discussed in the 75th difficult issue of the Nanjing (Classic of Difficulties).
3.1.2 Leftward deviation of the midline: The midline shifts toward the left side of the tongue (Figure 3-3), resulting in a smaller left side and a larger right side. This indicates left deficiency and right excess, specifically liver deficiency and lung excess, presenting a pattern of Metal subduing Wood. This reflects loss of lung qi dispersion and stagnation of both lung qi and large intestine qi, which may manifest as lung and large intestine disorders such as chest tightness, cough and wheezing, and sluggish or incomplete bowel movements. Liver deficiency may present as dry eyes, blurred vision, and discomfort in the rib-side region, as well as emotional symptoms such as sadness and depression.
The above two points also conform to the characteristic of the body’s qi mechanism — left ascent and right descent. Failure of left ascent results in stagnation on the left; failure of right descent results in stagnation on the right. Regulating disorders in the ascent and descent of qi on the left and right is a fundamental skill in diagnosis and treatment based on tongue examination.
3.1.3 Lateral curvature of a segment of the tongue midline (Figure 3-4: curvature of the cervicothoracic spine): This is commonly seen in spinal misalignment, scoliosis, or local muscle and fascia contractures affecting spinal balance. It can also be observed when the enlargement of internal organs deviates from their original positions, causing the midline to curve. Tumors within the chest or abdominal cavity, such as a large hepatic hemangioma, can also cause deviation of the midline.
3.1.4 Elevation or spot-like elevation of the tongue midline: This indicates localized obstruction of qi mechanism, such as in tumors or qi stagnation in a local organ. See Figure 3-5, which shows a patient with liver enlargement palpable four finger breadths below the costal margin.
3.1.5 Depression of the tongue midline: This indicates a localized deficiency of qi and blood, such as in sinking of middle qi. Additionally, surgical scars or organ resection can also cause localized depression of the tongue midline. Figure 3-6 shows a tongue image from a patient who underwent a hysterectomy, with a noticeable depression of the midline at the tongue root.
3.1.6 Deviation of the tongue midline to one side, especially when the tongue tip or body tilts to one side, suggests that a stroke has already occurred or is imminent (Figures 3-7, 3-8). Note the curvature in the cervicothoracic segment of this tongue midline (Figure 3-7), indicating scoliosis at the cervicothoracic junction.
3.1.7 Tilt of the midline, rather than a parallel shift, with the tongue body not curved. It is necessary to distinguish the conditions at the upper and lower ends of the midline, which can be broadly divided into two patterns:
First, the midline tilts from the upper right (tongue tip) to the lower left (tongue root). The pathogenesis is lung deficiency with large intestine excess, accompanied by liver deficiency and gallbladder excess (Figures 3-9, 3-10). Second, the midline tilts from the upper left (tongue tip) to the lower right (tongue root). The pathogenesis is the opposite of the above, i.e., lung excess (stagnation) with large intestine deficiency, accompanied by liver excess (stagnation) and gallbladder deficiency.
From the seven points above, it is clear that the tongue midline is of great significance. For any tongue examination, the first step is to draw or visually assess the tongue midline. Be sure to develop this habit.
3.2 Assessing Left-Right Qi Dysfunction from the Tongue Midline
One of the core principles of modern tongue diagnosis is the widely used TCM theory of “left ascent and right descent” of qi. The concept that qi in the human body ascends on the left and descends on the right was proposed by ancient sages based on observations of nature combined with yin-yang theory. The Suwen (Plain Questions) in Yin Yang Ying Xiang Da Lun states: “Left and right are the pathways of yin and yang.” The Suwen in Wu Yun Xing Da Lun also states: “That above moves to the right; that below moves to the left.” This refers to the mutual movement and communication of yin and yang qi in nature.
In terms of the circulation of yin and yang qi in the human meridians and zang-fu organs, although the lungs reside in the upper body and govern dispersing, their qi is descending and will pour down into the stomach. Therefore, the lungs are a yin organ within the yang. Although the liver resides in the lower body and governs smoothing and discharging, its qi is ascending and will penetrate the diaphragm to pour into the lungs. Therefore, the liver is a yang organ within yin. This shows that the upper-lower communication of yin and yang qi in the meridians and zang-fu organs is characterized by liver ascent and lung descent, which is also an observation made by our ancestors regarding the functions of the zang-fu organs and meridians. The left ascent and right descent of qi on the tongue is consistent with the ascent and descent of qi in the human body and has been validated clinically. The left half of the tongue corresponds to the liver, and the right half to the lungs. In clinical tongue diagnosis, by examining whether the left and right sides of the tongue are symmetrical in size and whether their thicknesses are consistent, one can determine whether the ascent and descent of qi in the liver, lungs, and the entire body are normal.
(To Be Continued)
作者：殷鴻春
3.1 舌中線定義（中文）
舌中線原本是一個解剖學名詞，沿著舌正面的中間縱向從舌尖向後劃一條線直達舌後根，這條線稱為舌中線 (見圖3-1)。正常的舌中線應在左右兩半舌的中間，且是筆直且無側彎、無偏凸、無上下彎曲、無裂紋及斷裂的。只要舌中線偏離了中間位置，或偏向左右，或上下起伏，或局部彎曲偏凸，即舌中線的平移、潛騰(凹凸)、歪斜、側凸、裂紋、斷裂等都具有中醫及西醫的病理意義。
劃舌中線時主要參考以下幾點: 一是要注意舌上自然形成的紋理，包括溝裂凹陷凸起，特別要注意舌尖及舌根處的最凹點及最凸點，這上下兩點往往是舌中線的終始點。二是查看舌左右的氣機是否真的偏盛偏衰到你畫的中線所代表的程度。若沒有明顯的氣機左右偏差，那麼就要舍去那些溝凹凸所標識的假中線，而是根據左右舌的中間線來設定中線的位置。舌中線的變動，是判斷人體氣機升降失常的最主要依據之一，也是最客觀可靠的依據。
其規則如下:
3.1.1. 中線右偏即中線向舌右側平移（圖3-2），舌左大右小，左實右虛，即肝實肺虛，呈現的是肝木侮肺金的象，同時木旺伐土而現脾土虛餒。肝實呈肝氣郁滯，患者見易生悶氣，脅肋脹悶不舒;肝郁克脾，易見脾虛症狀，如納呆、腹脹腹瀉或大便無力;肺虛則見咳、短氣不足以息等症。這實際上也是《難經》七十五難所謂 「東方實，西方虛」。
3.1.2. 中線左偏即中線向舌左側平移（圖3-3），舌左小右大，左虛右實，即肝虛肺實，金乘木的格局，為肺氣失宣，肺與大腸之氣均鬱滯，可見肺及大腸的病症，如胸悶咳喘大便不暢或不盡; 肝虛則見目澀、眼花、脅肋不舒等，情緒上可見悲傷抑鬱等症。
以上兩點也符合人體氣機左升右降的特點，左升不能乃郁在左，右降不能乃鬱在右。調理左右氣機升降失常是辨舌診治的入門功夫。
3.1.3.舌中線的某一段側彎（圖3-4 頸胸段脊柱側彎），常見於脊柱錯位、脊柱側彎及局部肌肉筋膜攣縮影響脊柱平衡，也可見於內臟器官腫大偏離原有位置，而造成中線側彎。胸腹腔內腫瘤，如巨大肝血管瘤，也可以出現中線的偏移。
3.1.4. 舌中線凸起或者點狀凸起，見於局部氣機被阻，如腫瘤、局部臟器的氣機鬱滯等，如圖3-5，這是一個肝肋下四橫指可觸及的肝大患者。
3.1.5. 舌中線凹陷，見於局部氣血虧虛，如中氣下陷。另外，手術瘢痕、臟器切除也可以出現局部舌中線凹陷。圖3-6就是一個子宮切除的舌象，舌根處中線明顯凹陷。
3.1.6.舌中線向一側偏斜，特別是舌尖或舌體歪向一側，考慮中風已發或者將發(圖3-7，圖3-8)。注意這個舌中線頸胸段有個彎曲，顯示頸胸椎交界處有側彎。
3.1.7. 中線歪斜，非平移， 舌體不歪斜，要區分中線上下兩端的情況而簡單分為兩種: 一是中線呈上(舌尖)右下(舌根)左斜，病機為肺虛大腸實伴肝虛膽實(圖 3-9，圖3-10)，二是上(舌尖)左下(舌根)右斜， 病機與前述情形正相反，為肺實(鬱)大腸虛伴肝實 (鬱)膽虛。
通過上述7點不難看出舌中線的意義非常重要，所有的舌象，看舌第一步就是畫舌中線或者目測舌中線，務必養成習慣。
3.2. 從舌中線看左右氣機失常（中文）
現代舌診應用原理之一就是中醫理論中最常用到的左升右降的原理。人體氣機左升右降是先人在觀察自然的基礎上結合陰陽理論提出的。《素問•陰陽應象大論》說:「左右者，陰陽之道路也」，《素問•五運行大論》也說:「上者右行，下者左行」，是指大自然陰陽二氣相互交通移動的情形。在上的天是由東向西，右轉運行，然後下降於地，在下的地是自西向東，左轉運行，然後上升至於天。這種大自然陰陽二氣的上下交通有「左升右降」 的現象，也是我們的祖先仰觀天文，俯察地理的觀察心得。
人體經脈臟腑中，以陰陽二氣互相交流的循行而言，肺雖居於上主宣發，但其氣是肅降的，會下注入胃，所以肺是陽中之陰髒; 肝雖位在下主疏泄，但其氣是升發的，會貫膈上注於肺，所以肝是陰中之陽髒。由此可知人體經脈臟腑陰陽二氣的上下交通是肝升肺降的，也是我們先人對臟腑經絡功能所作的觀察所得。舌的氣機左升右降與人體的氣機升降是 一致的，也是經過臨床檢驗的。舌的左半部分屬於肝，右半部分屬於肺，在舌診臨床中，主要查看左右舌的大小是否對稱，左右側厚薄是否一致，來判斷肝肺及人體氣機升降正常與否。
（未完待續）
