4 20 



ELEMENTAL Y ANA TOM F. 



[LESS. 



Thus they may all arise from the aorta in common as one 

 great trunk, subsequently dividing, as in the Ox ; or the left 

 carotid, subclavian, and vertebral arteries may all arise sepa- 

 rately from the aorta, as in the Dugong ; or both common 

 carotids may take origin in one trunk with the right sub- 

 clavian, as in the Lion ; or there may be two innominate 

 arteries, each dividing into subclavian and carotid, as in 

 the Hedgehog. 



FIG. 365. DIAGRAM REPRESENTING 

 THE'MAIN ARTERIES OF A BIRD 

 (FOWL), with the changes induced 

 on the primitive condition. 



(After H. Rathke.) 



a, a, internal carotids ; b, b, external 

 carotids ; c, g, common carotids ; d, 

 root of main aortic arch (here right); 

 e, arch of the same ; /, right sub- 

 clavian (which arises from the ana- 

 stomosis of the first two right primi- 

 tive aortic arches) \g, commencement 

 of the descending aorta ; /, //, left 

 subclavian ; /, z, t, pulmonary arte- 

 ries ; k, right, and /, left, rudiments 

 of the primitive aortic arches, 

 Nos. 5, 5, of Fig 358. 



FIG. 366. DIAGRAM REPRESENTING 

 THEMAIN ARTERIESOFA MAMMAL, 

 with the changes induced in the 

 primitive condition. 



(After H. Rathke. ) 



a, b, c, carotids, as before ; d, root of 

 main aortic arch (here left) ; c, arch 

 of the same ; f, commencement of 

 descending aorta ; g, left vertebral 

 artery ; h, left subclavian ; /, right 

 subclavian ; k, right vertebral artery; 

 /, continuation of right subclavian ; 

 m, pulmonary artery ; , remnant of 

 left primitive aortic arch < No. 5 of 

 Fig. 358), the ductus arteriosns or 

 ductus Botalli. 



The two common carotids may ascend in close juxta- 

 position, as in Birds, and one of them may be much reduced 

 in size, or even abort. 



The vertebral artery, instead of passing through the cer- 

 vical transverse processes, may perforate the neural lamina?, 

 as in the Llamas. 



The internal carotid may break up (inside the skull) into a 

 network of small arteries (called a rcte mirabile), as e.g. in 

 the Ox. 



