36 



the Conus arteriosus. The truncus bifurcated and each branch gave 

 rise to the three arterial arches, but owing to the displacement of the 

 ventricle the direction of the bifurcation was the reverse of the normal. 

 The posterior lobe, 10 mm by 6,5 mm was found to be the two auricles 

 into the left of which opened the pulmonary veins and into the right the 

 sinus venosus. In addition to the moving of the ventricle the sinus 

 venosus was much more posterior than is usually the case and the two 

 pre-caval veins opened into it just behind the auricles. This causes 

 the main trunks of the venous system and arterial system to cross 

 one another in a manner totally different from that in the normal frog 

 but apart from this both systems appeared to be quite normally con- 

 stituted (Fig. 2). 



Dissection showed that the auricles were completely divided but 

 the obliquely running septum appeared to be very thin. The opening 



Fis:. 1. 



Yh 



S.C.A. 



Fig. 1. Photograph of the heart in situ. L.A., Left Auricles; P.V.G., Posterior Vena 



Cava; T.,1., Truncus Arteriosus; T^, Ventricle. 

 Fig. 2. Diagram of the heart and main vessels. .4.. Aorta; Ä.V., Anterior Vena 

 Cava; B., Brachial Vein; C, Coeliaco-mesenteric; CO., Carotid gland; Cu., Cuta- 

 neous artery; E.C, External Cai-otid; E.J., External Jugular; H., Hepatic vein: 

 /., Innominate; I.C, Internal Carotid; I.J., Internal Jugular; L., Lingual vein; 

 L.A., Left Auricle; M., Mandibular vein; M.C, Musculo-Cutaneous; P., Pulmonary 

 vein; P.A., Pulmonary artery; P.C., Pulmo cutaneous; P.T.C, Posterior Vena cava: 

 R.A., Right Auricle; .S'.. Systemic Arch; S.C.A., Sub Clavian Artery; S.C.V., Sub 

 Clavian Vein; >S'.^'. Sub-scapular vein; Ä. F., Sinus venosus; T.^.. Truncus arterio- 

 sus; T'., Ventricle. 



into the ventricle was guarded in the usual manner by an auriculo- 

 ventricular valve with its tendinous threads. The conus also was normal 

 containing a spiral valve and guarded at its base by semi-lunar valves. 



