152 
MR. MARSHALL ON THE DEVELOPMENT 
Group C. A right vena cava superior, and a left cardiac venous trunk or coronary 
sinus. — This arrangement prevails in the higher Mammalia, as in the Whale*, Dol- 
phin* and Porpoise* among Cetacea, in the Seal-f-, Walrus*, Dog-f', Cat'j”, Tiger:}:, 
Hyaena:}:, Polecat -f- and Ermine:}: among Carnivora, in the Quadrumana, as for ex- 
ample, in two small species of Monkey'f'; and lastly, in the human subject. 
The left primitive trunk, now reduced to a cardiac vein, forms the coronary sinus, 
with its small oblique branch on the back of the left auricle, and having received the 
great coronary and some other cardiac veins, opens into the right auricle. The oblique 
vein is more or less evident in different cases. Thus it is large in the human sub- 
ject ; very apparent in the Dolphin, smaller in the Porpoise and the Dog, less evident 
in the Whale and Walrus, and very small in the Seal, Cat and Tiger §. The vestigial 
fold is more distinct in Man than in any animal which I have hitherto examined in 
the recent state ; but it is readily seen in the Monkey, Dog and Cat. 
Almost invariably the right azygos persists, whilst the lower intercostal veins of 
the left side, instead of forming a left azygos venous trunk, unite into an azygos 
minor which joins the right azygos. Variations in the extent of the azygos and azy- 
gos minor constitute subordinate peculiarities. In the Cetacea [j, the remarkable 
condition is found of total absence of the right azygos as well as of the left azygos 
vein. 
Peculiarities of the coronary vein and sinus in certain animals. — In the Ornitho- 
rhynchus, in which animal the left superior cava joins the inferior cava immediately 
before its termination in the right auricle, the coronary vein is said to open directly 
into the auricle by a separate orifice to the right of the inferior cava^. It seems not 
improbable that in this case the vein in question is rather a posterior cardiac vein, 
ascending upon the back of the ventricles, the vessel in the ordinary position of the 
coronary vein being diminished in size or absent. In very small animals having a 
left anterior venous trunk, as in the Mouse and Bat, I have observed that this condi- 
tion exists**. 
The arrangement of the valves of the coronary and other cardiac veins at their 
respective terminations in the coronary sinus, the left azygos trunk or the left vena 
cava superior, has already been examined and compared (pp. 133, 134). As to the 
Thebesian valve, it is present in every instance in which the left venous trunk forms 
* Preparations in Mus. Royal Coll. Surg. Lond. ; Whale, No. 135 ; Dolphin, No. 127 ; Porpoise, No. 130; 
Walrus, No. 76 ; Tiger, No. 68 : also Mus. University Coll. Lond. 
t The Author. I Bardeleben. 
§ Some of these observations have been made only on dried injected hearts. 
II Von Baer (Nova Acta Acad. Caes. Leop. Carol, vol. xvii. p. 408), also heart of the Whale, Mus, Royal 
Coll. Surg. Lond. Prep. No. 135. 
^ Meckel (quoted in Prof. Owen’s Art. Monotremata, Cycl. Anat. and Phys. p. 390). 
** It is also seen in the small heart of the common fowl, though in the larger heart of the Ostrich the coro- 
nary vein occupies its usual position and opens into the left superior cava (Owen, Art. Aves, Cycl. Anat. and 
Phys. vol. i. p. 330). 
