328 ANATOMICAL TECHNOLOGY. 



This is a conical prolongation of the base of the right ventricle at its 

 left corner, and is continued into the A. pulmonalis. In a heart of 

 average size its length is about 1 cm. Since there is no correspond- 

 ing prolongation of the left ventricle, the semilunar valves of the 

 aorta are upon a "lower" level than those of the A. pulmonalis, 

 i. e., they are nearer the apex of the ventricle (Fig. 94). The 

 ental surface of the conus is smooth. 



867. Ductus arteriosus (az.\ dct. art. (Fig. 92). By an over- 

 sight, this very significant remnant of an important foetal structure 

 is not represented upon any of the figures of actual preparations. 

 It is slight and easily overlooked in even a somewhat careful exam- 

 ination of the parts. We have never observed any depression cor- 

 responding with its attachment to the A. pulmonalis, and in the 

 aorta the depression is usually very indistinct. The ductus begins 

 at the cephalic side of the A. pulmonalis, just centrad of its bifurca- 

 tion, and extends very obliquely along the slight interval between 

 the artery and the aorta, to become attached to the latter a little 

 peripherad of the origin of the A. subclavia sinistra, and some- 

 what at the ventral as well as caudal side of the vessel. 



868. Fossa ovalis (az.\ Fs. ov. The oval depression upon the 

 right side of the septum auriculare (Fig. 91). This is not dis- 

 tinctly represented upon any of the figures of actual preparations. 

 It is most easily seen after the lateral wall of each auricle has been 

 removed and the septum is held between the eye and the light. At 

 about the middle of the septum there will appear a thinner area, 

 bounded cephalad and ventrad by a more or less distinct thicken- 

 ing. The thin portion is usually oval, and measures about 5x2.5 

 mm. In the kitten before birth, the thin area is more or less com- 

 pletely absent, so that the two auricles communicate, and the blood 

 from the postcava passes through the orifice, the Fm. ovale, into the 

 left ventricle. Respecting the significance of the fossa ovalis and its 

 appearance in the human heart, see the works cited and also Quain, 

 A, II, 799-803, and Dalton, A, 699. 



On the left side of the septum, the area corresponding with the 

 position of the Fs. ovalis is sometimes quite smooth, but more often 

 presents (as in Prep. 360, Museum of Cornell University) a crescentic 

 elevation at its dorsal side. 



869. Hemicardia dextra The right side or portion of the 

 heart. Since the entire organ is called heart or cardia, it is logi- 

 cally incorrect to speak of the two sides as the right heart and the 



