ANATOMY OF THE OPHIDIA. 41 



1906.] 



example three other veins of the same kind, of which two received 

 branches from the gut ; there was also an independent gastro- 

 hepatic vessel, as is shown in the accompanynig figure (text- 

 fio- 1 1 , p. 40), which represents the liver- veins of this example. The 

 em'o-astric vein sends, at any rate, two branches to the liver, which 

 are very anterior in position: one of these receives a branch from 

 the stomach before entering the liver. In another example there 

 were only three dorsal parieto-hepatics. It was m this example 

 that a branch from the epigastric joined the umbilical vein, as 

 referred to above. In a third specimen, I saw only two parieto- 

 hepatic vessels, arising, as in the others, from the left side of the 

 dorsal median line. In this and other cases the differences may 

 not be real, but due to absence of blood in the vessels at the time 

 of examination. _ . /^ i • v i 



The orio-in of the hinder mesenteric vein m the Ophidia has 

 been variously stated, the different modes of origin described 

 possibly corresponding to the different species and genera 

 examined. Hochstetter* describes and figures Tropidonotus 

 natrix (with which he finds Coluber cesculajni to agree) as 

 possessing a mesenteric vein which arises from both afferent 

 renals, the two branches combining to form the single vein. 

 I have not been able to ascertain to my satisfaction the arrange- 

 ment of these veins in Bitis nasicornis; but in another Yiper, 

 Aoicistrodon piscivortts, I have found that each renal afferent vein 

 gives off a branch, and that these join to form the mesenteric 

 vein running along the lower surface of the large intestine. The 

 arrangement characteristic of this Yiper is therefore precisely that 

 of Tropidonotus and Coluber. 



(5) Considerations respecting the Primitive Structttre 

 of the Lungs in the Squamata. 



Eatteria (or, indeed, most Lacertilians) on the one hand, and 

 such a snake as Causus rhombeatus on the other, represent the two 

 extremes of modification of the Squamate lung. In the former 

 the lungs are paired and equal, and are effective breathing- organs 

 throughout : they are separated from the glottis by a long stretch of 

 trachea, and by two equisized bronchi into which the trachea divides 

 some way in front of the lungs. In the Yiper, on the other 

 hand, the trachea opens into the lung but a short way behind the 

 glottis, down which it is continued as an open gutter ; at, or about, 

 the level of the heart the lung becomes anangious and is a mere 

 air-sac ; while there is no trace of a second lung, or of a division 

 of the tracheal gutter into two bronchial tubes. It is undoubtedly 

 the prevalent opinion that of these two extremes, that represented 

 by Eatteria is near to the primitive Sauropsidan lung, while the 

 lung of Causios represents the most modified type. Paradoxical 

 though it will appear, there are reasons founded upon anatomical 



* Morph. Jahrb. xix. 1893, p. 489, pi. xvi. fig. 19. 



