I90 THE SALAMANDER 



proximal row, while numerous trabeculae pass across their concave 

 aspects from the wall of the truncus. The bulbus cordis is cardiac in 

 origin, its muscular walls being of the same nature as, and continuous 

 with, the ventricle. 



The truncus arteriosus (t.a.) represents a greatly shortened ventral 

 aorta enclosed in a sheath of cardiac muscle which grows forwards 

 round it from the bulbus, the tissue pertinent to the truncus itself 

 being arterial tissue containing unstriped muscle-fibres. The sheath 

 of cardiac muscle envelops the whole of the truncus posterior to the 

 aortic arches, and it is prolonged in the middle line so as to form a 

 strap passing between the carotid arches from the dorsal to the ven- 

 tral side. On the dorsal side, within the cavity thus formed between 

 the strap and the truncus, is the central lymph heart (cf. p. 260). 

 Ziillich did not realize the true significance of the lymph heart and 

 strap, but describes it as an 'elastische Polster', and says (p. 205), 

 'Die funktionelle Bedeutung scheint lediglich die zu sein, das dieses 

 elastische Kissen den abgehenden Arterien Schutz gegen Knickung 

 gewahrt, bzw. eine nachgiebige, federnde Abstutzung gegen den 

 dorsal daruberliegenden Osophagus bietet.' He does not appear to 

 have been acquainted with Greil's work, although he states that the 

 'Polster' contains lymph. 



As regards the cavity of the truncus arteriosus, two regions are 

 discernible; a short undivided section next to the bulbus cordis — 

 the truncus impar — and the main section which gives rise to the eight 

 aortae by the ingrowth of septa from its walls. These septa have 

 received different names from various authors. Greil's nomenclature 

 is adopted here, and it is not thought necessary to give other syno- 

 nyms as they are quite obvious. The septum between the carotid 

 arches is the septum caroticum\ that separating the carotid from the 

 systemic arch on either side the septum carotico-aorticum ; the septum 

 aortico-pulmonale divides the systemic arch from the 'third' arch, and 

 the latter is in turn separated from the pulmonary arch by the 

 septum accessorium. The septum pulmonale separates the right pul- 

 monary arch from the left. It should be noted that there is no great 

 prolongation of the horizontal septum so as to divide the chamber 

 into a cavum pulmo-aorticum and a cavum aortico-caroticum as there 

 is in the Frog. In fact there is no well-marked difference in the 

 length of any of the septa, and they may not be quite symmetrical on 

 the two sides. The septum pulmonale is the longest and is closely 

 followed by the septa aortico-pulmonale and caroticum, while the 

 septa carotico-aortica and the septa accessoria are shorter and approxi- 

 mately equal to one another in length. 



