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responding surface of the ceratohyal, where it lies, as in Amia, close 

 to the dorsal (internal) edge of the element. In Salmo and Esox, 

 and also in many other teleosts, the artery is said by Maurer (1888) 

 to have a course relative to the hypo- and ceratohyals similar to that 

 in Scomber, but in these fishes the artery is said to later perforate 

 the hyomandibular, which it does not do in Scomber. In the mail- 

 cheeked fishes the artery is said by Allen (1905, p. 47) to reach the 

 hyoid arch from the "inside", a Kttle behind the hypohyals, and then 

 to run along "the dorsal surface of the cerato- and epi-hyals". 

 I, however, find the artery in Trigla running forward over the dorsal 

 (internal) edge of the hypohyal, close to its proximal end, and then 

 upward and backward near the dorsal (internal) edge of the antero- 

 lateral surface of that element and then of the ceratohyal, beyond 

 which latter element it has a course strictly similar to that in Scomber. 

 The artery accordingly crosses the ventral (external) surface of the 

 cartilaginous or osseous elements of the hyoidean arch in Polyodon 

 and Amia, perforates those elements in 'Scomber, Salmo and certain 

 other teleosts, and crosses their dorsal (internal) surface in the mail- 

 cheeked fishes. These varying relations of the artery to the arch 

 are however all quite unquestionably due, as Maurer has fully ex- 

 plained for Salmo, to the fact that the artery is developed, and pulled 

 back from the mandibular into the hyoidean arch, before the chondri- 

 fication of the elements of the latter arch, these chondrifications 

 accordingly taking place in certain cases in normal relations, dorsal 

 to the artery, in others enveloping and enclosing the artery, and in 

 still others lying wholly ventral to the artery. The position of the 

 artery, in Polyodon, is probably more primitive than that in any of the 

 other fishes mentioned, its position along the ventral (external) edge 

 of the ceratohyal being one that it would naturally acquire when 

 pulled backward into the hyoidean arch. In all the other fishes the 

 artery has slipped off this external edge of the ceratohyal on to the 

 antero-lateral surface of the element. 



The pseudobranch of Polyodon has, as is well known, the position 

 -of a mandibular and not of a hyoidean gill. The spiracular canal 

 begins at the dorso-anterior end of the first gill opening and is not 

 visible on the dorsal surface of the mouth cavity unless the parts are 

 pulled apart. Immediately beyond its opening the canal expands into 

 a chamber, and on the floor of this chamber, on its antero-lateral wall, 

 is the pseudobranch; the filaments of the organ beginning slightly 

 within the opening that leads into the chamber and being directed 

 antero - laterally. From the dorso - lateral portion of the chamber 

 the spiracular canal is continued upward along the lateral surface 



