AORTIC ARCHES OF BIRDS — GLENNY 



545 



2. Bicarotidinae abnormales: One of the dorsal carotids enters the hypapophysial 



canal, while the complimentary vessel of the opposite side remains as a 

 superficial vessel. This condition is of infrequent ordinal occurrence but is 

 very common among the parrots, in which group the right vessel enters the 

 hypapophysial canal in most instances. 



3. Bicarotidinae infranormales: Both dorsal carotids are superficial and lie along 



the ventral face of the neck. This condition is of rare occurrence. Despite 

 the fact that it had been presumed to exist (Meckel, 1826), it was not dis- 

 covered until 1952 when Glenny observed it in Zanclostomus and Phae- 

 nicophaeus and a further modification of it in Ramphococcyx. These vessels 

 were found to send small branches to the oesophagus. 



/ 



Jf 



# 



Figure 1 10. — Points of origin and types of the coracoid or sternoclavicular and thoracic 

 or intercostal arteries (ventral views, left side only). Type of coracoid indicated by 

 capital letter, type of thoracic indicated by numeral (for code see pp. 543,544): a, A-1; 

 b, B-1; c, C-1; d, D-6; e, E-1;/, F-1; g, A-2; h, A-3; t, A-4; ;, C-5. 



