Truncus Arteriosus. 199 



the Melbourne University, also to Mr. John Booth and Mr. J. 

 C. Gihnour, for the live specimens they have been at trouble 

 to procure for me, thus aiding me in investigation with the dis- 

 Becting microscope. 



As regards the nomenclature of the valves to be dealt with 

 hereafter, as no definite names appear to have been hitherto 

 applied to them, 1 have called those between the Ventricle and 

 the Pylangium the 'pylangiaJ ralve-^, and those between the 

 Pylangium and Synangium, the xyncniyial. 



The accompanying table will serve to show the discrepancies in 

 the accounts of the valves of the truncus arteriosus given l)y 

 certain authors. 



The interior of the trtmcus, as is well known, is divided into 

 two parts — the proximal, called the ryhnigium, and the distal, 

 the Synatiginm.^ In some species the line of demarcation be- 

 tween these two portions of the Trunctis Arteriosus is very dis- 

 tinct externally (Fig. 2), while in others — e.g., Hyla aurea 

 (Fig. I ) — there is little or no outward evidence of the division 

 into proximal and distal compartments. 



Just to the left of the opening from the ventricle, a dorsally 

 attached septa arises, running the whole length of the Pylangium, 

 and called, from the spiral twist in it, the spiral valve or fold. 

 This spiral valve is free ventrally, and normally turns from the 

 right side at the posterior end, to the left at the anterior. At 

 the anterior end of the valve there are more or less well marked 

 valves guarding the entrance to the Pulmo cutaneous arch. 



The Synangium is that part of the truncus which is anterior 

 to the spiral valve, and from it arise the systemic and carotid 

 arches. The spiral fold is a constant feature, differing only as 

 to shape and relative thickness in the various genera. The 

 valves at the anterior end of the spiral fold, separating the 

 Pylangium from the Synangium, while constantly present, are 



1 Different authors ai«i)ly different names to the parts associated with what we call 

 the Tnuicun arteriosus. Marshall, whom we follow, calls the whole structure the 

 Truncus arteriosus, and divides it into a proximal part, the Pylangium, and a distal, the 

 Synangium. Howes confines the term Truncus to the proximal part; Parker and 

 Haswell call tiie proximal part tlie Conus arteriosus and the distal bnlbus aortae ; Holmes 

 calls the proximal part the Indbus cordis, and the distal the Truncus arteriosus, whilst 

 Ecker calls the proximal part the Truncus, though he sometimes applies the same name 

 to the combined proximal and distal parts. 



Sa 



