534 NOTE ON THE VENOUS S"?STEM OF BIEDS. 



saltern Ficum viridem, cujus quidem generis alias species tres, 

 P. martium, P. major em, et P. medium, una tantum vena jugulari 

 et quidem dextra prseditas esse Eathkius docet, non hue, sed ad 

 regulam secundam pertinentem cognovi." 



I conceive it is quite possible Barkow miglit have made the 

 error of supposing only one vein present, if his observations had 

 been conducted on such a bird as the Short-tailed Tit, or even 

 on a spirit specimen of a less distinctly atrophied bird. Still 

 more might he have been misled in case of a Sparrow ; for in this 

 bird {Passer domesticus) but the veriest rudiment of the left vein 

 exists, and it ceases to be a tubular structure at about half the 

 length of the cervix from its origin. I very carefully threw a blue 

 injection into the vessel from the transverse trunk at the skull-base, 

 and got the fluid to run as a fine line so far as I have stated, 

 where it was stayed by a blind ending of the vein, which beneath 

 this point was indistinguishable from the fatty and connective 

 tissue with which the pneumogastric nerve was associated. 



In the only example of the Robin {Erithacus rubecula) I have 

 had the fortune to examine, the two vessels showed a consider- 

 ably greater disproportion than that figured by Neugebaur, a fact 

 which leads me to think that age may, to great extent, determine 

 the obliteration of an organ in natural atrophy ; i. e. in this par- 

 ticular instance a young bird will possess a less-attenuated left 

 jugular vein than an adult. 



Examination of developmental changes, however, will afford 

 much information in this matter ; and I anticipate we shall find 

 the growing embryo to exhibit gradations varying from equality 

 in the size of the veins to the adult differences already noted. 

 This would be in agreement with Von Baer's law of progress from 

 the general to the special ; for it is a fact worth knowing that 

 all the birds, so far, exhibiting this considerable suppression of 

 the left jugular vein have been from Prof. Huxley's division of 

 the ^githognathse. Moreover Alectoromorphous birds show gra- 

 dations of structure varying from close equality to differences as 

 as much as one to three, beyond which they would seem not to 

 approach the group named above. 



How far the peculiarities I have described are structural adap- 

 tations subserving function, I hope to be able to speak with some 

 authority later, as also regarding their full morphological import. 

 I can do no more now than state my full conviction that they 

 possess a definite meaning, and one to be determined by the spe- 



