1887.] 



The Brachial Arterial Arches in Birds. 



429 



Time. 



0' 0" Condenser connected to battery. 



30 Condenser quickly discharged and connected with electro- 



meter. 



Reading on scale 539 



1 „ 615 maximum. 



2 „ 557 



3 „ 544 



Other liquids were tested in this way, but in no other case were 

 similar phenomena observed. Mixtures of CS 2 and benzene or 

 paraffin were also inactive in this sense, even when the mixtures 

 were incomplete and the liquids were put in in such a way as to be 

 " streaky," as was found possible. 



Some attempts were made to discover traces of polarisation, but no 

 definite results were obtained. In the earliest experiments something 

 of the kind was observed, but this was traced to the key and con- 

 nexions. 



XXII. " The Development of the Branchial Arterial Arches in 

 Birds, with special Reference to the Origin of the Sub- 

 clavian and Carotids." By John Yule Mackay, M.D., 

 Senior Demonstrator of Anatomy, University of Glasgow. 

 Communicated by Professor Cleland, M.D., F.R.S. Re- 

 ceived May 29, 1887. 



(Abstract.) 



According to the theories of Rathke, which are universally accepted 

 at the present day, the subclavian artery is supposed to take its origin 

 from the aortic root or fourth embryonic branchial arterial arch. In 

 the adult bird the subclavian on each side is found springing from 

 the extremity of an innominate artery along with the common carotid. 

 It is presumed that the right subclavian has been, by a shortening of 

 the aortic arch, carried forwards until it meets and fuses with the base 

 of the common carotid artery ; and the left subclavian is regarded as 

 representing by its basal portion the fourth left arch or left primitive 

 aorta. The subclavian of birds is thus regarded by Rathke as being 

 developed in a manner similar to that of mammals. The author 

 points out, however, that there is a marked difference in the rela- 

 tions of the artery to the surrounding parts in these two groups. In 

 mammals the subclavian artery is Grossed on its ventral aspect by the 

 jugular vein and the pneumogastric nerve, and the recurrent branch 

 of the latter turns round it upon the right side, but in birds the nerve 



