612 MR. c. H. o'donoghue on the 



had been lost and the margin was regenerating. Text-fig. 85 illus- 

 trates how far this process had extended. It will be seen that 

 the restitutive prohferations were most active along the free distal 

 margin of the fin. Here several (four) eminences were present, each 

 suggesting the pointed tip of the fin ; there can, however, be no 

 doubt as to which of these is the terminal one, since the skeleton 

 of the fin can be followed into the lowest of these lappets. The 

 case is evidently akin to one known to teratologists, for when 

 certain areas in injured limbs of batrachians are stimulated, there 

 appears Polydactyly or polypody. It may therefore be worthy of 

 record that a similar condition occurs in the lung-fish Ceratodus. 



33, The Circulatory System o£ the Common Grass-Snake 

 (Tropido7iotus natrix). By Chas. H. O'Donoghue, 

 B.Sc, F.Z.S., Assistant to the Jodrell Professor o£ 

 Zoology, University College, London. 



[Received April 1, 1912 : Read April 23, 1912.] 

 (Plates LXX.-LXXII. and Text-figures 86-91.) 



Index. 



Page 

 I. Introduction 612 



II. The Heart. 



A. Development 614 



B. Adult Form 617 



III. The Arterial System. 



A. Development 619 



B. Adult Form 621 



(a) Anterior Vessels 621 



(6) Posterior Vessels 623 



IV. The Venous System. 



A. Development 626 



B. Adult Form 630 



{a) Anterior Vessels 630 



(6) Posterior Vessels 631 



V. The Vessels of the Head. 



A. Arteries 635 



B. Veins 640 



VI. List of References 643 



VII. Explanation of Plates 645 



I. Introduction. 



Our knowledge of the circulatory system in snakes is far from 

 exhaustive ; indeed, we have only a complete account of the 

 vessels in the Python by Hopkinson and Pancoat (25), and a 

 later and a more full one by Jaquart (26), and in Pelophilus 

 madagascariensis hy Gadoyv * . Although Tropidonotus natrix is 



* This is incorporated in the account given by Hoffmann (23). 



