Dictionary of Ichthyology  

copula = 2) united basibranchials in sharks. 
Visceral arch of Scyllium (= Scyliorhinus), BH = basihyal, C = copula (united basibranchials), E = epihyal, H = hypohyal, HM = hyomandibula, HY = hyoid, K = keratobranchial, P = pharyngobranchial, from Kingsley's "Textbook of Vertebrate Zoology, 1906. Photograph by Brian W. Coad.

           Canadian Museum of Nature
         www.briancoad.com