the corresponding structure of the rest of the Mammalia are two: in the first place, the valve itself does not completely surround the ostium; it is only developed on one side; the septal half (_i.e._ that turned towards the interventricular septum) is either entirely absent or more generally represented by a small bit of membrane; nevertheless I found[35] recently in an _Ornithorhynchus_ heart a complete septal half to the right auriculo-ventricular valve. The second point of interest in connexion with this valve is, that the musculi papillares instead of ending in chordae tendineae attached to the free edge of the valve are directly attached to the valve, and in some cases pass through its membranous flap, to be attached to its origin at the boundary of the auricle and of the ventricle. The invading of the valve-flap by muscle in this way is highly interesting, as it recalls the heart of the bird and of the crocodile. The imperfect condition of the valve (from which, as has already been stated, the septal half is as a rule nearly absent) is a point of resemblance to the heart of the bird; the corresponding valve of the crocodile's heart being complete. {67} [Illustration] FIG. 43.--_Lepus cuniculus._ Ventral view of the vascular system. The heart is somewhat displaced towards the left of the subject; the arteries of the right and the veins of the left side are in great measure removed. _a.epg_, internal mammary artery; _a.f_, anterior facial vein; _a.m_, anterior mesenteric artery; _a.ph_, anterior phrenic vein; _az.v_, azygos vein; _br_, brachial artery; _c.il.a_, common iliac artery; _c.il.v_, common iliac vein; _coe_, coeliac artery; _d.ao_, dorsal aorta: _e.c_, external carotid artery; _e.il.a_, external iliac artery; _e.il.v_, external iliac vein; _e.ju_, external jugular vein; _fm.a_, femoral artery; _fm.v_, femoral vein; _h.v_, hepatic veins; _i.c_, internal carotid artery; _i.cs_, intercostal vessels; _i.il.a_, internal iliac artery; _i.il.v_, internal iliac vein; _i.ju_, internal jugular vein; _i.l_, iliolumbar artery and vein; _in_, innominate artery; _l.au_, left auricle; _l.c.c_; left common carotid artery; _l.pr.c_, left pre-caval vein; _l.v_, left ventricle; _m.sc_, median sacral artery; _p.a_, pulmonary artery; _p.epg_, epigastric artery and vein; _p.f_, posterior facial vein; _p.m_, posterior mesenteric artery; _p.ph_, posterior phrenic veins; _pt.c_, post-caval vein; _p.v_, pulmonary vein; _r_, renal artery and vein; _r.au_, right auricle; _r.c.c_, right common carotid artery; _r.prc_, right pre-caval vein; _r.v_, right ventricle; _s.cl.a_, right subclavian artery; _s.cl.v_, subclavian vein; _spm_, spermatic artery; _s.vs_, vesical artery; _ut_, uterine artery and vein; _vr_, vertebral artery. (From Parker's _Zootomy_.)