Hi MJWayne,
Instead of using artificial sinew, which always looks artificial, use waxed linen thread. You can order large spools of it, or you can get small amounts from Tandy Leather. You can also use real sinew though you usually have to process it a bit yourself to get the smaller pieces to sew with out of the larger patch of sinew.
Tandy also has a great book available called "Handsewing Leather" by Al Stohlman (same guy who makes the really spendy leather working tools). If you don't already have all the tools get their basic kit that comes with the book and some decent tools as well as the waxed linen thread.
For sewing leather garments a welted seam is the most durable. This involves sewing a piece of leather (a welt) in between the two pieces of leather you are joining. Then you trim the welt close and turn the seam inside out. Looks very neat and trim, is historically accurate and super durable. It's the same method used with much thicker leather to make knife sheaths so the knife blade doesn't cut the stitching.
For more info on various methods of sewing leather garments look at the last few chapters in Deerskins to Buckskins 2nd edition by Matt Richards. Lots of great info there. The book is about brain tanning leather and then has a section on how to make garments out of your braintanned hides.
Twisted_1in66 :thumbsup: