154 
MR. MARSHALL ON THE DEVELOPMENT 
when the viscera are transposed ; so that transposition, as an additional cause of 
peculiarity, may affect any of the preceding groups. 
Lastly, the three principal groups may present subordinate variations, depending 
on peculiarities either in the upper vena cava itself, or in the azygos veins, or in the 
coronary vein of the heart. 
In the second class of varieties, in which no cross branch is formed in the neck, 
both of the lateral primitive veins are necessarily persistent, each carrying back the 
blood of its own side. Such cases may also present peculiarities in the azygos system, 
or may be complicated by transposition of the heart. 
Though the records of the varieties in these great veins in the human subject do 
not as yet supply examples of every conceivable deviation, and though the descrip- 
tions of many are somewhat obscure or incomplete, they appear to admit of arrange- 
ment according to the scheme just mentioned. 
CLASS I. TRANSVERSE BRANCH IN THE NECK, PRESENT. 
Group A. The second anterior venous trunk reduced to a cardiac venous trunk. 
a. Without transposition. A right vena cava superior, and a left cardiac venous 
trunk or coronary ^ww^.-^This is the ordinary condition of the great anterior veins. It 
is accompanied by numberless subordinate modifications, occurring either in the right 
superior cava itself, or in the azygos systems, oi- in the coronary vein of the heart, and 
includes by far the greater number of the recorded varieties of these veins. 
a. V arieties in the Right Superior Vena Cava. 
These appear to be very rare. A presumed example is recorded by Rosenthal*, 
in which, the auricles and ventricles being undivided, two superior veins, called two 
superior cavse, joined immediately before ending in the single auricle, into which 
however they opened by separate mouths. In this case the upper cava may have 
been shorter than usual, so that the two superior veins were the venae innominatae ; 
but the description is not sufficiently full-f”. 
b. Varieties in the Right and Left Azygos Systems. 
These are exceedingly numerous, and require to be referred to several heads: — 
1. The right intercostal system consolidated, the left intercostal system broken up . — 
In this, the most frequent arrangement, the right intercostal veins end principally in 
the azygos vein, but partly also in a right superior intercostal vein. The left inter- 
* Abhandl. aus dem Gebiete der Anat. Physiol, und Pathol. Berlin, 1824, p. 150. 
t It maybe here mentioned that Weese (De Ectopia Cordis, &c, 1818, Berolin. sect. 37, 48) has twice 
found the left innominate vein (the primitive cross branch) in malformed foetuses, passing across the neck be- 
hind the trachea and oesophagus. 
