Silken Thomas - the first with descendants in part of The Body (4,6)
I believe the answer is:
soft tissue
'part of the body' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.
'silken thomas the first with descendants' is the wordplay.
'silken thomas' becomes 'soft' (I can't justify this - if you can you should give a lot more credence to this answer).
'the first' becomes 't' (sst letter of 'the').
'with' says to put letters next to each other.
'descendants' becomes 'issue' (I've seen this in another clue).
'soft'+'t'+'issue'='SOFT TISSUE'
'in' is the link.
Can you help me to learn more?
(Another definition for soft tissue that I've seen is " Parts of the body".)