CIRCULATING SYSTEM OF BIRDS. 



185 



The fibrine in the blood of Birds is soft and very lacerable. 

 The serum is usually of a light yellow colour, but is golden in 

 the Cathartes atratus. Dr. Jones notices the strong musky 

 odour of the blood of this Vulture, like that of the living bird.' 



§ 153. Heart of Birds. — This organ consists of two ventricles 

 and two auricles ; the septum of both being complete. 



The form of the heart is always that of a cone, sometimes wide 

 and short, as in the Ostrich and Crane ; sometimes more elon- 

 gated, as in the Emeu, fig. 90, 

 and Vulture; or still more 

 acute, as in the Curlew and 

 Common Fowl. 



Its situation is more anterior 

 and mesial than in Mammalia, 

 and its axis is always parallel 

 with the axis of the trunk. It 

 is not contained with the lungs 

 in an especial cavity, but its 

 apex is lodged between the 

 lobes of the liver ; the dia- 

 phragm, as a rule, not being 

 so far developed as to separate 

 the chest from the abdomen. 



As the lungs are confined to 

 the dorsal part of the chest, the 

 whole of the anterior surface 

 of the pericardium is exposed 



when the sternum of the bird is removed. The pericardium is 

 thin, but of a firm texture, and adheres by its external surface to 

 the surrounding air-cells. It is of considerable size, and commonly 

 prolonged for some way between the lobes of the liver. 



The auricles of the heart in Birds have not externally such 

 free appendices as in Mammals. The right auricle is much 

 larger than the left ; it is more distinctly divided internally into 

 a sinus, ib. d, and auricle proper, Z», z, x, than in Mammals, and 

 these parts are separated by a more complete valvular structure, 

 but less definitely developed than in the Crocodile. 



Three veins terminate in the sinus, there being in Birds always 

 two precavals, as in Reptiles. The right precaval, ib. a, which 

 returns the blood from the right wing and right side of the neck, 

 terminates in the upper and anterior part of the sinus ; the left 



Heart of the Emeu. 



* CCXLV. p. 16. 



