目的    观察椎动脉第3段垂直段（V3v）与第2颈神经（C2N）毗邻关系，为椎动脉型颈椎病(Cervical spondylotic arteriopathy, CSA)及枕颈痛合并眩晕的发生机制提供形态学依据。  方法    头颈标本33侧，解剖剥离法显露C2N和V3v及其相邻的结构，观测V3v与C2N交叉部位，范围及形态。  结果    所有标本中V3v与C2N前支均为横向交叉，跨越椎动脉后方（33/33，100%）。依据其接触程度可分为3种类型：①接触性交叉：C2N的前支依其条索状原形与V3v横向交叉，共6侧占18.2%；②压痕性交叉：C2N横跨V3v段呈扁带状或纵向凹痕状，共7侧占21.2%；③半缠绕压扁带性交叉：C2N前支呈扁带状横向半环形缠绕V3v，共20侧占60.6%。交叉处呈直角交叉16侧占48.5%。V3v交叉前和交叉处管径分别为（3.82±0.07） mm、（3.35±0.05） mm；交叉前和交叉处C2N前支宽径为（2.38±0.05） mm、（3.53±0.09） mm。交叉处距中线距离（23.25±0.39） mm；交叉处距同侧寰枢外侧关节囊距离（6.26±0.2） mm；距同侧C2-3关节突关节距离（11.78±0.3） mm。  结论    V3v与C2N前支形成横向交叉性接触，其中以半缠绕压扁带性交叉为主，这种毗邻关系可能使C2N前支压迫V3v使大脑供血减少，可能是CSA发生机制之一和/或高血压合并枕颈痛的形态学基础。

Objective  To observe the adjacent relationship between V3v and C2N  so as to provide morphological basis for the pathogenesis of cervical spondylotic arteriopathy (CSA) and both occipitocervical  pain combined with vertigo.   Methods   Thirty-three sides of head-neck specimens were selected for this investigation. The anatomical dissecting and stripping methods were used to expose the C2N and V3v and the adjacent structure. The crossing part of C2N and V3v, range and morphology were observed. Results   The anterior branch of C2N run laterally and crossed with V3v posteriorly in all specimen (33/33, 100%). According to the degree of contacts between C2N and V3v, these crossing relations could be divided into as three types: ① Simple contact crossing type: The original cord-shape anterior branch of C2N crossed with V3v laterally, with a total of 6 sides accounting for 18.2% ; ②Indentation crossing type: The segment of anterior branch of C2N which was crossing with V3v was in flat or longitudinal indentation shape, with a total of 7 sides accounting for 21.2%; ③Semi-circular wrapped crossing type: the anterior branch of C2N become flattened and wrapped the V3v in semi-circular way, with a total of 20 sides accounting for 60.6% . The anterior branches of C2N and V3v crossed each other in 16 sides at right angles, accounting for 48.5%. The diameters of V3v approaching to the crossing part and the crossing part were (3.82±0.07) mm and (3.35±0.05) mm, respectively. The width- diameter of the anterior branch of C2N approaching to the crossing part and the crossing part were (2.38±0.05) mm and (3.53±0.09) mm, respectively. The distances between intersection part and central line was (23.25±0.39) mm, the distance from crossing part to the ipsilateral lateral atlantoaxial joint was (6.26±0.2) mm, and the distance to the ipsilateral zygapophysial joint of C2 and C3 was (11.78±0.3) mm.    Conclusions   The anterior branch of the C2N formed three transverse crossing relationships with V3v, the dominant one among them is the semi-circular wrapped crossing type, this closing adjacent relations may lead the anterior branch of C2N to compresse V3v and may reduce the blood supply to the brain, it may be one of the pathogenesis of CSA and/or may be the morphological basis of hypertension with occipitocervical pain.