THE VASCULAR SYSTEM 231 



The mesial branch of the lejt side continues directly forwards, in- 

 cHned sHghtly mesiad, and enters the junction of the post-caval and 

 sinus venosus. The mesial branch of the right side also passes for- 

 wards to the pericardial margin and then turns abruptly to the left 

 around the apex of the pericardium and joins its fellow on the left side 

 just as it enters the post-caval. The lateral branches of the anterior 

 epigastric veins are symmetrical, so that the description of one will 

 serve for both. It accompanies the artery and turns sharply dorsal- 

 wards to the region of the axilla, where it joins the V. lateralis and the 

 V. brachialis medialis. On its way it receives two important factors : 



(i) V . pectoralis (v.pect.) from the muscle of the same name, as well 

 as from the M. coraco-brachialis brevis. The factor from the latter 

 can be traced right down the muscle into the arm, where it appears 

 to form a direct continuation of the V. anastomotica brachii (see 

 also p. 235). 



(ii) One or two VV. cutaneae from the skin of the axilla. 



The exact pattern of the junction of the vessel with the V. lateralis 

 and V. brachialis medialis is somewhat variable, but usually the V. 

 lateralis and anterior epigastric vein first join to form a short common 

 trunk, a V. axillaris (v.ax.), and then receive the vein from the arm. 



The vessel just described is called the epigastric vein in Crypto- 

 branchus (Osawa) and Rana (Gaupp).i In the Salamander it is norm- 

 ally larger than the mesial branch of the anterior epigastric vein and 

 therefore carries most of the blood from that vessel. Nevertheless 

 it seems quite probable that it actually represents a 'V. coraco-pec- 

 toralis' which should be regarded as a factor of the V. axillaris that 

 has become secondarily associated with the V. epigastrica anterior 

 by fusion with a factor of the latter vein, the association becoming 

 increasingly stronger during phylogeny until it finally provides the 

 only path of egress for the blood from the epigastric vein. Such an 

 hypothesis is rendered the more probable in that it allows a simple 

 explanation of the direct connexion between the anterior epigastric 

 veins and the sinus venosus in Salamander, which would otherwise be 

 somewhat puzzling. 



As is well known from the work of Goette, Hochstetter, and 

 others, the abdominal vein in Amphibia develops by the fusion of 

 a pair of lateral vessels connected anteriorly with the sinus venosus 

 or ductus Cuvieri and posteriorly with the iliac veins. In the Frog 

 the former connexion normally disappears while the latter develops 



' In these animals there is no connexion between the anterior epigastric vein and the 

 sinus venosus, although it is possible that one may exist in Cryptobranchus but has been 

 overlooked by Osawa. It is very easily destroyed in opening the animal. 



