FOSSIL AND RECENT 135 



dermosphenotic. Posteriorly the otic canal joins the preopercular canal and the 

 supratemporal commissure at the postero-lateral angle of the pterotic. The lateral 

 line passes back through the supratemporal to open on the undersurface of that bone. 



The infraorbital canal runs within the large infraorbital trough. Anteriorly the 

 canal splits into two branches : dorsally there is a short antorbital branch which 

 runs over the antorbital and ends blindly at the dorsal end of that element ; anteriorly 

 an ' ethmoid ' branch runs through the rostral ossicles before passing through the 

 premaxilla to end blindly within that bone. The triradiate union of the ' ethmoid ' 

 branch, antorbital branch and the main infraorbital canal lies in the skin just anterior 

 to the first infraorbital. At one point, above the gap between the middle and 

 posterior rostral ossicles, the ' ethmoid ' canal and supraorbital canals are only 

 separated by membrane. 



The course of the preopercular sensory canal has been described above. Ventrally 

 this canal continues within the deep trough upon the dentary and articular as the 

 mandibular sensory canal. 



Hyoid arch and gill arches. The ceratohyal is separated by a band of cartilage 

 into a semicircular posterior element and a longer, waisted anterior ceratohyal. 

 Two hypohyals are represented by perichondral ossifications around a single large 

 cartilage. The smaller dorsal hypohyal articulates with the posterior face of the 

 basihyal and the ventral hypohyal receives a ligament from the urohyal. The 

 afferent hyoidean artery pierces the medial surface of the ventral hypohyal and 

 passes into a groove on the lateral surface of the anterior and part of the posterior 

 ceratohyal. Six branchiostegal rays are attached to the medial surface of the 

 ceratohyal elements. The uppermost (posterior) ray is the only member of the series 

 associated with the posterior ceratohyal. 



The basibranchium is formed by a partially ossified basihyal and three separately 

 ossified basibranchials. The fourth basibranchial is entirely cartilaginous. The 

 basihyal tooth plate is large and bears approximately 15 pointed teeth posteriorly. 

 A large tooth plate overlies the first three basibranchials and like the fourth basi- 

 branchial tooth plate bears teeth similar to those upon the basihyal tooth plate. 

 The teeth associated with the basibranchium become smaller posteriorly. 



The first two hypobranchials articulate with the posterior surface of their respective 

 basibranchials. The reduced third hypobranchial articulates with the centre of its 

 basibranchial. Of the five ceratobranchials the first three articulate with the distal 

 ends of the hypobranchials while the fourth and fifth are connected to the fourth 

 basibranchial by ligaments. 



The dorsal arch elements are represented by epibranchials, infra- and supra- 

 pharyngobranchials. There are four epibranchials associated with the first four 

 ceratobranchials. The first epibranchial is simple, showing a double articulatory 

 head. The anteriorly directed head receives the posterior end of the small rectangu- 

 lar first infrapharyngobranchial. The posterior head of the epibranchial is directed 

 dorso-medially and articulates with a cartilaginous first suprapharyngobranchial. 

 The second epibranchial, like the third, shows a marked bifid head with the anteriorly 

 directed limb being larger than the dorso-medially directed process. The anterior 

 head articulates with the posterior margin, or in the case of the third epibranchial 



