pectoral girdle and run posteriorly the term "subcutaneous vessels " 



If one takes the position that because the subcutaneous vessels of 

 the Teleostei are not homologous with those of the Plecostei 9 the teleosts 

 do not. have subcutaneous vessels,, why tnen did Kishinouye apply the term 

 subcutaneous vessels to nonhomologous vessels in the Plecostei? And 

 furthermore, supposing that the subcutaneous vessels of the teleosts and 

 those of the Plecostei cannot be regarded as identical embryologically, 

 then insofar as there is no embryclogical proof regarding the subcutaneous 

 vessels of the various species of the Plecostei it is not in a strict 

 sense permissible to say that they are homologous vessels The reason 

 for this is that in vertebrates in the case of the segmental vessels, 

 vertebral nerves, myotomes, and similar parts which as a rule form a 

 segmental arrangement it is not generally possible without some embryo.logi- 

 cal facts for a basis to consider as homologous things -which occur in 

 different body segments . For example, it cannot be denied that there is 

 a great deal of room for doubt as to whether the subcutaneous vessels 

 which comes out from beneath the fifth vertebra in Thurmus j^ermo and that 

 which originates under the ninth vertebra in iJeothunnus ma crop berus are 

 after all embryologically homologous , 



Further supposing that the subcutaneous artery of Gnathagnus elongatus 

 described above does differ from that of the Plecostei and that, because 

 it does not originate directly from the dorsal aorta, it cannot be called 

 a subcutaneous vessel, then it must be made clear why all of the sub- 

 cutaneous veins of the Plecostei are called subcutaneous veins regardless 

 of the striking differences in their points of origin and their relation- 

 ships to the major vessels . 



Since as a matter of fact the subcutaneous artery of Gnathagnus 

 elonga tus does not originate directly from the dorsal aorta but rather 

 from the basal portion of the subclavicular artery, it may perhaps be 

 that it is not fundamentally identical with the subcutaneous arteries of 

 the Plecostei, however, considering the question from the opposite point 

 of view, blood vessels are generally prone to variation and it is not at 

 all strange that homologous vessels should differ greatly as between species 

 and markedly as between individuals. 



Now to give a few examples of such variation, in the ruminants and 

 the Peris sodactyla the left end right subclavicular arteries and the 

 cervical arteries are fused in their basal portions to form a truncus 

 communis o In the carnivores, marsupials, and in swine only the left 

 subclavicular artery is separate from the truncus communisj, while in the 

 Chir optera , porpoises, and Neophocaena phocaenoides the right and left 

 subclavicular arteries, although they are fused at their bases to the 

 corresponding cervical arteries, do not form a common trunk as in the 

 animals mentioned above. In man, the anthropoid apes, the duckbilled 

 platypus, seals, the .Edentata , and the fin whale the basal portions of 

 the right subclavicular artery and the corresponding cervical artery are 

 joined into a single vessel while the same vessels on the left side are 

 completely separate. 



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