548 PROCEEDINGS OF THE NATIONAL MUSEUM vol. io4 



Class B 



B-1 Conjuncto-carotidinae normales. 



B-2-d Conjuncto-carotidinae abnormales: right side reduced. 



B-2-S Conjuncto-carotidinae abnormales: left side reduced. 



B-3a-d Ligamentum carotidinae-conjuncti: partial lumen; ligament on the 



right side. 

 B-3a-s Ligamentum carotidinae-conjuncti: partial lumen; ligament on the 



left side. 

 B-3b-d Ligamentum carotidinae-conjuncti: entire, on right side. 

 B-3b-s Ligamentum carotidinae-conjuncti: entire, on left side. 

 B-4-d Dextro-carotidinae normales: right carotid alone enters the hypapo- 



physial canal. 

 B-4-S Laevo-carotidinae normales: left carotid alone enters the hypapo- 



physial canal. 

 B-5-d Dextro-carotidinae infranormales: right carotid is superficial (left is 



lacking). 

 B-5-S Laevo-carotidinae infranormales: left carotid is superficial (right is 



lacking) . 

 B-6a-d Ligamentum unicarotidinae (ligamentum ottleyi): entire, right side. 

 B-6a-s Ligamentum unicarotidinae (ligamentum ottleyi): entire, left side. 

 B-6b-d Ligamentum unicarotidinae: incomplete or lacking, right side. 

 B-6b-s Ligamentum unicarotidinae: incomplete or lacking, left side. 



By means of this codified classification, all birds can be placed in 

 one of two major groups with respect to the adult carotid arrangement, 

 and these in turn may then be further subdivided to show their ap- 

 parent value with respect to levels of evolution and possible phyletic 

 relationships. Furthermore, this carotid classification may be used 

 to show both species evolution and, ontogenetically, the course of 

 changes which took place during embryonic development. 



This scheme has the advantage of being able to show where large 

 (macro) or small (micro) steps in avian evolution of the aortic arch 

 system has taken place. It also has the particular advantage of 

 demonstrating the probable ontogenetic course of events which took 

 place within any single or individual specimen. 



Arterial arrangement-patterns in neck and thorax 

 Class AVES 



Basically bicarotid. Several functional and structural modifica- 

 tions are found in both families and orders. 



As in other amniotes, the carotid, systemic, and pulmonary arches 

 alone remain as functional derivatives of the embryonic aortic arches. 

 The left ligamentum botalli atrophies and may become incorporated 

 into the ligamentum aortae or it may be completely resorbed. The 

 right ligamentum botalli may remain as a persistent vestige of the 

 ductus botalli or it may be reduced to a ligamentous "button"; it 

 may be incorporated into the wall of the right radix aortae or be 

 completely resorbed. 



