72 



ALLEN 



there was no communication with the venous system here, and 

 have satisfied myself in every case that this is simply a blind 

 sac. The third division (c) is merely a much smaller blind sac, 

 lying behind (b). At about this level the pericardial sinus 

 receives a small lymphatic vessel from the side, which comes 

 from the center of the clavicle (Figs. 4 and 6, C.L. V.). In 

 this region it is important to avoid confusing the external 

 subclavian and anterior gastric or oesophagus veins (Fig. 6, 

 J?. Sub. V. and A. Gas. V.) with the lymphatics. The external 

 subclavian vein crosses over the pericardial sinus and its divi- 

 sions {a, b and c) to discharge itself in the precava ; while the 

 anterior gastric veins pass under the pericardial sinus, but over 

 its divisions (a, b and c) and likewise empty into the precava. 

 There is always quite a prominence in the neighborhood of the 

 anterior ventral corner of the pericardial sinus which extends 

 outward and forward some little distance between the external 

 and internal pharyngo-clavicularis muscles. 



From a lateral view what appears to be a separate posterior 

 pericardial sinus (Figs. 4 and 6, Per.S. m ) emptying into the 

 main pericardial sinus is shown in a ventral view (Figs. 9 and 

 10, Pcr.S.( Y) ) to be nothing more than a posterior continuation 

 of the main pericardial sinus. Each of these so-called posterior 

 pericardial sinuses or posterior continuations of the main peri- 

 cardial sinuses passes at first ventrad behind the sinus venosus 

 and ventricle, being separated from them only by the pericar- 

 dium, and when the posterior ventral corner of the ventricle is 

 reached curves backward at nearly right angles. At this point 

 in about half of the specimens a connecting branch (Fig. 6 and 

 10, X) was given off cephalad to anastomose with a papilla of 

 the ventral pericardial sinus (Figs. 6 and 10, P. V.Pcr.S.) that 

 communicates with the main pericardial sinus. In an equal 

 number of specimens connecting vessel (X) was absent (see 

 Figs. 4 and 9), and possibly it should be noted that in these 

 specimens the ventral pericardial sinus papilla always followed 

 very close to the posterior portion of the main pericardial sinus. 

 Both of the posterior pericardial sinuses or posterior portions of 

 the main pericardial sinuses continue backward some little dis- 

 tance, gradually increasing in size as they approach one another, 



