Bipennate

From - + pennate.

Full definition of bipennate

(medicine, anatomy, zoology) Of, pertaining to, or having the nature of a muscle, the fibres of which attach to a tendon on two sides (as a feather barbed on both sides).

1999, Christopher McGowan, A Practical Guide to Vertebrate Mechanics,It then follows that bipennate muscles generate even more force than unipennate ones of similar volume, and the force increases with the angle of pennation.
2007, Neal S. Elattrache, Christopher D. Harner, Raffy Mirzayan, Jon K. Sekiya (editors), Surgical Techniques in Sports Medicine, page 50,Beneath the deltoid lies the external rotators of the shoulders, including the bipennate infraspinatus and the teres minor (Fig. 5-20B).
2008, John O'Neill, Musculoskeletal Ultrasound: Anatomy and Technique, page 4,Bipennate muscles have a central tendon with oblique insertion fibers on both sides, eg, the rectus femoris (Figure 1.3c).

1849, Adrien de Jussieu, James Hewetson Wilson, The Elements of Botany, insects&hl=en&ei=UR0oTs3bJ87KiAKhi8GABw&sa=X&oi=book_result&ct=result&resnum=8&ved=0CEwQ6AEwBw#v=onepage&q=%22bipennate%22%20insect|insects&f=false page 501,Its bipennate leaves are composed of a slightly straightened general petiole, of four partial petioles, situated, two at the extremity of the proceeding, and convergent, two a little lower, and growing almost at right angles; each of them bearing more than twenty pairs of small horizontal petioles.
1897, William Thomas Fernie, Herbal Simples Approved for Modern Uses of Cure, 2006 Gutenberg eBook edition,But this Burnet Pimpinella is of a different (Umbelliferous) order, though similarly styled because its leaves are likewise bipennate.