614 MR, c. H. o'bonoghue on the 



For the sake of clearness in description, the account of the 

 blood-vessels of the head is not included in the general description 

 of the vascular system of the whole animal, but is dealt with 

 separately later. A brief account of the development of the 

 heart and of the arterial and venous systems has been introduced 

 in order to throw some light on the condition that obtains in the 

 adult. 



Two or three features of general interest in connection with 

 the elongation of the body and the loss of limbs in the Ophidia 

 are clearly brought out in dealing with the vascular system of the 

 Grass-Snake. The first is the marked asymmetry of the viscera 

 and their blood-supply ; not only are the organs of the right side 

 anterior to those of the left, but they are also considerably larger. 

 Thus the right ovary, supra-renal body, and the kidney are in 

 front of and larger than the corresponding organs oh the left, 

 and, as is well known, in the case of the lungs the left one is 

 entirely suppressed. 



Secondly, the tendency to form longitudinal systems of vessels, 

 common to all Ophidia, as Beddard (1) pointed out, is well 

 marked. The various arteries supplying the intestine and the 

 fat-bodies are in each instance indirectly connected into one long 

 system. The ovarian artery forms a longitudinal trunk along the 

 corresponding supra-renal body. Among the veins also we find 

 that the hepatic portal vein runs from one end of the intestine 

 to the other, and that each oviduct possesses a sinus running 

 beside it for the greater part of its length. This oviducal sinus 

 is veiy conspicuous in T. natrix, although it does not appear to 

 have been described previously in other snakes. The liver, too, 

 is greatly elongated, and the post-caval vein and the hepatic 

 portal vein pass along its opposite faces from one end to the 

 other. 



Lastly, the blood-vessels of the adult, with the exception of a 

 small pair of veins in the cloacal region, which may represent the 

 pelvic veins of Lacertilia, give no indication of their derivation 

 from those of a limb-bearing ancestor. 



In conclusion I should like to express my sincere thanks to 

 Professor J. P. Hill of this College for the kindly assistance and 

 advice he has given me throughout the work. 



II. The Heart, (PI. LXX.) 

 (A) Develop')nent. 



The development of the heart has been very fully dealt with 

 by Rathke (30), and as this account difiers but slightly from that 

 of Lacerta given by Greil (18) and Hochstetter (20), it does not 

 appear necessary to give more than a brief outline here. 



The primitive heart is in the form of a simple tube stretching 

 in an antero-posterior direction in the region of the gill-slits. 

 Its posterior end is formed by the union of the two omphalo- 



