part of part of has part has part has_part bounding layer of bounding layer of surrounds surrounds collagen trimer theca cell layer theca externa Wikipedia:Theca_externa SCTID:258767003 theca externa (folliculus ovaricus tertiarius) tunica externa of theca folliculi ovary theca externa MA:0001713 UBERON:0000156 FMA:18657 The theca externa is the outer layers of the theca folliculi. It contains abundant collagen and is mainly supportive. UBERON:0005182 external coat of theca folliculi BTO:0002852 theca interna membranous layer reproductive structure