35J4 ANATOMICAL TECHNOLOGY. 



and the heart lies between them ; physiologically, the lungs form a single organ which is 

 interposed between the two hearts ; Wilder, 1. 



§ 846. The diagram (Fig. 92) differs from an accurate representation of any actual 

 section of the cat's heart in the following respects : — 



I. The separation of the right and left portions {hemicardicB), involving the splitting 

 of the septa aitriculare et veiitrievlare and the elongation of the ductus arteriosus. 



3. The non-crossing 6f the aorta and A. pvlmonalis and the deflection of the former to 

 the right instead of the left. 



3. The representation of the cardiac (coronary) vessels by the beginnings of the two 

 arteries and the ends of two of the veins. 



4. The representation of the systemic veins {postcaoa, prcecava andF. azygos) by a single 

 vessel here named V. cava. 



5. The representation of the several W. pulmonales by a single vessel. 



6. The representation of the two lungs by a single and simple sac. 



7. The distance from one another upon the arcus aorticvs of the origins of the vessels 

 supplying the head and arms, AA. ircKhio-cephalica et subclaxia sinistra {A. hreph., A. 

 sbclv.). 



8. The representation of the branches and capillaries of the aorta and A. pulmonalis by 

 only tltree divisions of each vessel. 



9. The representation of the semilunar and auricula -ventricular valves in each case by 

 a pair of lines. 



10. The omission of the fret-work upon the ental aspect of the walls, especially of the 

 ventricles and the auricular appendices. 



II. The positions and points of attachment of the appendices and of the veins which 

 enter the auricles have been assigned with a view to convenience of representation rather 

 than absolute accuracy. 



13. The omission of the ductus thoracicus, which might have been made to join the 

 proximal portion of the Vena cava. 



§ 847. The right and left portions {hemicardi(B) of the heart agree with each other in 

 the following respects : — 



1. Their primary division into an auricle (auricula), which is relatively cephalic in posi- 

 tion, irregular, rounded and thin walled ; and a ventricle (ventricalus), which is caudal in 

 positioii, regular, pointed and thick walled. 



3. The division of each auricle into a larger sinus and a smaller appendix. 



3. The communication of eacli auricle with its ventricle by a slightly constricted orifice, 

 guarded by valves of irregular shape. 



4. The attachment of cusps of the free edges of the auriculo-ventricular valves to the 

 ventricular walls by fibrous chordae tendinem springing from the apices of columnce carnea. 



5. The free communication of the auricles vrith veins ( VV. cavm and YY. pulmonariai), 



6. The exit from the ventricles of arteries {aorta and A. pulmonalis). 



7. The guarding of each arterial orifice by three similar and regular semilunar valves. 



8. The expansion of each artery opposite the valves to form three sinuses of Yalsalva. 



9. The aorta and A. pulmonalis are united by a fibrous band, the ductus arteriosus, 

 the normally impervious remnant of a vessel which, in the foetus, permitted the blood to 

 pass from the latter vessel into the former peripherad of the origin of the vessels {AA. 

 brachio-cepJmlica et suhclavia sinistra) which carried the purer maternal blood to the head 

 and arms. 



§ 848. The right and left portions {hemicardim) of the heart differ in the following 

 respects : — 



