1906.] SYSTEM OF CERTAIN SPECIES OF ANURA. 1033 



remainder. The pulmonary portion at once bifurcated and the 

 posterior branch of it immediately afterwards gave back a small 

 vessel to the rectum which crossed the I'ectal arteiy dorsally. The 

 same branch divided again before reaching the lung ; the other 

 did not. 



The vein from this lung was about equal in bulk to the two 

 arterial branches combined. It left the apex of the lung as a 

 single vessel, and entered the extreme rectal branch of the 

 vena portm at a point almost coincident with the origin of the 

 pulmonary artery. It was wrapped up closely with the two 

 branches of the latter in a simple peritoneal sheath, so closely, 

 that it required the greatest care in dissection to ascertain the 

 true arrangement of the vessels ; and the same was the case in 

 the arteries of the right lung, the separating out of the component 

 factors being only due to the necessity of so figuring them. 



It is to be observed in the present instance that the two arteries 

 commence early to subdivide, and produce between them no less 

 than seven branches before reaching in either case a point at the 

 apex of the king where the bi'anches are still practically non- 

 divergent. In the circumstances, the occurrence of such a 

 consistent process of division within an extremely narrow compass 

 seems to deserve particular notice from an ontogenetic point 

 of view, suggesting the interpretation that the arteries them- 

 selves show a predisposition to revert to a remotely ancient type 

 in which such division was necessitated by the character and 

 extent of their destination in the swim-bladder. 



In view of the present and similar examples, the question is to 



be considered whether the abnormality described above in Bufo 



horeas may not fall within the same category as representing an 



intermediate condition such as that exhibited in the Dipnoan fish 



Protopterus, where the pulmonary ai'teries have a very similar 



origin. 



T.1 ii T7 • if-n 100-7 L. R. CrAWSHAY.1 



Plymouth, Feo. l7tn, 1907. -^ 



LETTEEING OP TEXT-FIGURES. 



an. Anastomosis between Aa. mesenterica anterior and mesenterica inferior. 



ao. Aorta. 



b.c. A. bulhi cordis. 



a. A. coeUaca. 



c.a. Artery to Corpora adiposa. 



c.e. A. carotis externa. 



c.Ji. Artery to M. coraco-humeralis. 



c.i, A. carotis interna, 



c.il.e. A. circumflexa ilium externa, 



c.il.i. A. circtmiflexa ilium interna, 



c.f.l. A. cutanea femoris lateralis, 



cm. A. cutanea magna, 



co.i. Artery to M. coccygeo-iliacus. 



cu.li. Artery to skin of upper arm. 



cu.]}. Artery to skin under pectoral girdle. 



cy. Aa. cysticoe. 



ev. A. epigastrico-vesioalis. 



68* 



