346 RECONSTRUCTION MODEL OF A HORSE EMBRYO TWENTY-ONE DAYS OLD. 



KEY TO LETTERING OF FIGURES ON PLATE XIX. 



[1AA. First aortic arch. 

 •J.I .!. Sordini aortic arch. 

 .1/. Allantois. 

 Alii. Allantoic branches of aorta. 

 All). Allantoic diverticulum. 

 AIM. Allantoic mesoderm. 



Am. Amnion. 

 ACV. Anterior cardinal vein. 

 . I ii.i. Anastomoses, between allantoic 

 arteries and umbilical veins. 

 APpC. Arrow u in pleuro-pericardial 

 canal. 

 .1 T. Atrium. 

 . I I ' '. Atrio- ventricular canal. 



1JJA. 1st branchial arch 

 ■Hi A. 2nd 

 3BA. 3rd 

 iBA. 4th „ 



BO. Bulbus cordis. 

 1BC. 1st branchial cleft. 

 2BC. 2nd branchial cleft. 



BM. Bucco-pharyngeal membrane. 

 IBP. 1st branchial pouch. 

 IBP. 2nd „ 



3BP. 3rd 

 iBP. 4th 



CI. Cloaca. 

 CN. Caudal neuroporc. 



DA. Dorsal aorta. 

 DC. Duct of Cuvier. 



FB. Fore-brain. 



HB. Hind-brain. 

 HG. Hind-gut. 



Im. Rudiment of lungs. 



MB. Mid-brain. 



Nc. Notochord. 

 NeC. Neural canal. 



OV. Otic vesicle. 

 OtV. Otic vesicle. 



PCV. Posterior cardinal vein. 

 PoV. Primary optic vesicle. 

 Ppr. Pleuro-pericardial ridge. 



Sm. Somatopleure. 

 Sp. Splanchnopleure. 

 SpM. Spinal medulla. 

 SV. Sinus venosus. 



TA. Truncus aorticus. 

 TI. Tuberculum impar. 

 TS. Terminal sinus. 



TJV . Umbilical vein. 



V. Ventricle. 

 VV . Vitelline vein. 



For ZBP, fig. 55, read 2BP. 



