228 Mr Lancliester and Mr TJiacker, Preliminary Note on 



Preliminary Note on the Superior Vena Cava of the Cat. By 

 W, F. Lanchester, M.A,, King's College, and A. G. Thacker. 



[Read 22 November, 1920.] 



The present series of observations arose out of the more or less 

 accidental discovery of a discrepancy between the factors of the 

 Superior Vena Cava in a cat that we were dissecting and the 

 description of these veins given in St George Mivart's well-known 

 text-book on the Cat. It will be remembered that in the cat the 

 two innominate veins (or, as they are otherwise called, the brachio- 

 cephalic veins) are formed by the union, on either side, of the 

 External Jugulars and Subclavians, the two Innominates then 

 uniting with each other slightly to the right of the trachea to form 

 the single Superior Vena Cava. The right Innominate is of course 

 the anterior portion of the surviving Superior Vena Cava. Now, 

 according to Mivart's description, the Internal Jugular (of either 

 side) runs into the corresponding Innominate. In our first cat we 

 found on the contrary that the Internal Jugular ran into the 

 External Jugular, or in other words, that the vein which unites 

 with the Subclavian is not really an External Jugular but a Com- 

 mon Jugular. There are several American text-books on the cat, 

 and we found that they agreed with our own first observations, 

 but none of them refer to the different description given by 

 Mivart, neither do any of them mention another vein, which does 

 in fact usually join the Innominate (on one side only) at the point 

 Mivart indicates for the Internal Jugular and which is usually 

 much more conspicuous in dissection than the Internal Jugular 

 itself. This is the vein coming from the thyroid glands, which, 

 though it is of course a paired structure in the anterior, is usually 

 single in the posterior part of its course. We decided to clear up 

 this small point regarding the position of the Internal Jugular. 

 The American text-books are correct. Out of 30 cats dissected, in 

 29 the Internal Jugular entered the External Jugular before the 

 union of the latter with the Subclavian. In one small kitten the 

 three veins — the Subclavian, the External Jugular, and the Internal 

 Jugular — appeared to meet one another at the same point. Our 

 observations show, therefore, that there is normally a Common 

 Jugular in the cat, and this vein is often of considerable length. 

 It is often longer, sometimes much longer, than the corresponding 

 Innominate. The Thyroidean, as stated, usually falls into one or 

 other of the Innominates ; but it sometimes falls into the Common 

 Jugular or even into the Internal Jugular. In two cases the 

 Thyroideans were separate throughout their course. 



