:5o 



DIPNOI 



twisted conns of Ceratodus, one is so enlarged as to longitudinally 



divide the cavity into two channels. 



— a4 



lr~- 



--at 



Fig. '21'.'. 

 Krefft. Ventral view of tin- heart 



In the Dipneumones, and 

 especially in Lepidosirev, 

 where this subdivision 

 of the cavities of the 

 heart is more completely 

 carried out, these valves 

 fuse to a longitudinal 

 fold. The pulmonary 

 blood entering the left 

 side of the atrium is 

 thus borne forward to 

 the first two aortic 

 arches, and the venous 

 blood to the last two 

 (Figs. 218, 221). 



From the truncus 

 arteriosus, the short 

 remnant of the ventral 

 aorta, spring four pairs 

 of afferent branchial 

 vessels, passing up the 

 first four branchial 

 arches. Four corre- 

 sponding pairs of epi- 

 branchial arteries are 

 formed by the junction 

 of two efferent vessels 

 in each arch in Ceratodus 

 (Fig. 220). They join the 

 dorsal aorta. From the 

 posterior epibranchial, 

 the sixth aortic arch, 

 counting the mandibular 

 as the first, is given off 

 a pulmonary artery to 

 the air-bladder. The 



torsleri, Krefft. ventral view of the heart c ™ 



dissected so as to expos." tin' inside of the ventricle and presence 01 tWO erterent 



conns, and the disposition of the aortic arches, a*- 1 *, four ,. QO „„i„ :„ oor-Vi Kran/»>iinl 



aortic arches, a dotted line passes up the base of the 1st vessels 111 eacn Oiantlll.U 



and combined 3rd and 4th; at, atrium; c, cut wall of ], ar m l^otll the Dipnoi 



conns; /'. plug tilling tin' atrio-ventricular opening; Iv, ... . r , 



small posterior valves ; p, portion of wall of pericardium ; and the Selachll IS prob- 



-.-■, specialised row of enlarged valves; t, truncus; r, , , ( n\*-c\r\rTav**+ln 



anterior valve, also cut wall of ventricle; w and z, dotted ably 01 110 pil) lOgeilCUC 



lines passing into the sinus venosus. (Compare Fig. 218, gjo-nificance ' in the l'ela- 



p. 249.) & -> 



tion of the epibranchial 

 arches to the bars the Dipnoi are the more normal (p. 111). On 

 the other band, the reduction of the ventral aorta, the gathering 



