#5711 PTB *sya-n ⪤ *sin FLESH / ANIMAL / BODY / AGENTIVE NOMINALIZER
This richly attested root must be considered distinct from #530 PTB *r‑sa VEIN / SINEW / INTERNAL CHANNEL / PULSE, although certain forms (especially those meaning ‘muscle’) seem to show overlap between the two roots.
The ‑n suffix is directly attested in Jingpho, Geman/Kaman, and Chinese.
This morpheme appears as a prefix in numerous animal names and words for parts of the body. See HPTB:102 and STC:106-108.
We are positing an allofamic relationship between the forms with medial *‑ya‑ and *‑i‑. See HPTB: 278, 306, 449.