Sentence:  But what is most worthy of notice is, that the greater number of muscular fibres arising from the coracoid and radio-ulnar bones form a pectoral muscle, superficial to the other fibres of the great lateral, and <WSD>digitating</WSD> with them along the side of the fish opposite the extremities of the fifth, sixth, seventh, and eighth ribs. 
Meaning of the word marked with <WSD> tags:  To spread out from a common point in a finger-like manner.