指哪个？

A 72-year-old man presented with a T1N0M0 squamous cell carcinoma of the right posterior buccal mucosa/retromolar region. He underwent prophylactic selective neck dissection (level 1–4) of the right neck as part of ablative and reconstructive surgery for this cancer. During the level 2–4 neck dissection, a posterior tributary was seen draining into the IJV from the medial aspect of sternocleidomastoid muscle (SCM) going antero-inferiorly joining the lower third of the IJV.

IJV 颈内静脉

72岁男性，右后颊粘膜/磨牙后区鳞状细胞癌（T1N0M0），作为这种癌症的切除和重建手术的一部分，行预防性择期右颈淋巴结清扫术（1-4级）。在2-4级颈淋巴结清扫术中，可见从胸锁乳突肌（sternocleidomastoid muscle，SCM）内侧向前下方走向的一支后支静脉汇入IJV的下1/3（图1）。

 from the medial aspect of sternocleidomastoid muscle (SCM) 是指  IJV  还是指 a posterior tributary？谢谢