7 



nected posteriorly to the diaphragm, but partially separated from it by 

 the oesophagus : on laying it open, the heart is exposed, with the great 

 vessels starting from it. On the surface of the organ are seen the 

 two coronary arteries, one arising behind the infundibulum of the 

 pulmonary artery, and passing first between the left auricle and ven- 

 tricle, then between the two ventricles anteriorly ; the other, arising 

 from the aorta, opposite the right side of the pulmonary artery, and pass- 

 ing in the posterior auriculo -ventricular sulcus, supplies the back of the 

 heart, anastomosing with the last at the apex. 



The right auricle is a medium- sized cavity, with well-marked verti- 

 cal musculi pectinati in its wall, and no appendix. The inter- auricular 

 septum is thick, and separates the right from the smaller left auricle, 

 which also presents strong perpendicular muscular bands on its wall, and 

 is likewise devoid of an appendix. The two pulmonary veins unite 

 and open into this cavity, on its posterior wall, by one common aper- 

 ture, which is surrounded by a strong muscular band, which would be 

 competent to close the orifice in a valvular manner. To the outer sur- 

 face of the auricle several fatty masses are appended, like the appen- 

 dices epiploics of the intestines. 



The right ventricle is a three-sided pyramid in shape when distended, 

 smooth inside except around its edge, where there are a series of mus- 

 cular trabecular ; its auricular orifice is oval, about 1 J inch in its long 

 axis, and guarded by a strong muscular valve, Inline thick, situated to the 

 rightof the foramen, and extending for two -thirds around it; astrong mus- 

 cular band unites this to the anterior wall of the cavity, and strengthens 

 its attachment. Numerous foraminse Thebesians exist on the inner sur- 

 face of this cavity. The orifice of the pulmonary artery is about two inches 

 from the right auriculo -ventricular opening, and is guarded by three semi- 

 lunar valves with indistinct corpora Arantii, and having large sinuses of 

 Valsalva behind them. 



The left ventricle is strong, its wall being thirteen lines thick in 

 several places, near the apex, however, it is extremely thin, in one spot 

 only measuring two lines. The left auriculo-ventricular opening has a 

 strong zona tendinosa and three membranous valves attached by cords 

 tendines, but without distinct musculi papilares connected to them : 

 carnes columns are apparent near the apex of this cavity, but are not 

 connected to the valves. The cords tendines are very numerous, and 

 pass transversely outwards from the walls of the cavity to the valves, the 

 curtains of which are situated right, left, and posterior; the first is the 

 largest, and is placed half an inch from the auricular opening. The aortic 

 orificepresents nothing peculiar, but is protected by three semilunar valves. 

 Longitudinal rugs were visible in the lining membrane of the aorta in 

 the female ostrich, with patches of atheromatous deposit. 



The aorta passes from its origin to the right side, and then curves 

 backwards and to the left ; this arch ascends for a very short distance, 

 and about an inch above its origin from its convexity it gives off two 

 arteris innominats, right and left, the latter being on a plane anterior to 

 the former, and both lying on the trachea, in front of which and above 

 the aorta lies a large round air cavity, about two inches and a half in 



