44 ON THE ANATOMY OF THE OPHIDIA. [Jan. 16, 



pulmonary artery and vein of Bitis nasicornis *, that both artery 

 and vein bifurcate soon after leaving, or just before enteiung, the 

 heart. One branch goes to, or comes from, the anterior tracheal 

 part of the lung, while the other branch has a similar relation to 

 the thoracic part of the continuous lung. It seems to me that this 

 anatomical fact explains two other facts which have been a little 

 difficult to me hitherto. 



The trachea in Snakes, and in certain Lizards at any rate, is closely 

 accompanied by arteries or an artery which is one of tlie systemic 

 branches. This carotid artery is concerned with the blood-supply 

 of the windpipe and adjacent organs and regions. In some cases, 

 however (probably much more generally than I am at present in 

 a position to know), the trachea is accompanied by arteries which 

 arise not from the systemic arteries but f I'om the pulmonary. I have 

 shown this to be the case in Gerrhosaurus f and more recently 

 in Hatteria J. In both of these Saurians the artery in question 

 is most clearly a branch of the pulmonary, and equally clearly 

 lies alongside of the windpipe anteriorly. A careless dissection 

 would fail to show this, as I consider it, highly important point. 

 It is, however, plain when the artery is properly followed out in 

 an injected specimen. 



Now the pulmonary artery is, it is hardly necessary to say, a 

 respiratory artery ; it is concerned, that is to say, not with the 

 nutritive supply of the lung-tissue but with the oxygenation of 

 the blood. The tissues of the lung receive their nutritive supply 

 from elsewhere. Branches from the aorta supply this need which 

 have no relation whatever to the special respiratoiy arteries and 

 veins. This is, of course, universally ti-ue of the higher vei'tebrates. 

 It seems therefore that the persistence of a branch of the pulmonary 

 artery supplying the trachea, taken in conjunction with the 

 bifurcating pulmonary artery of the Yiper with its ti-acheal and 

 thoracic portions of the lung, is a fact which decidedly points in 

 the direction of a previous i-espiratory function of that part of 

 the respiratory passage which it now supplies. 



The assumption upon the various facts which have been briefly 

 dealt with in the course of the preceding remarks, that the most 

 primitive type of Squamate lung is most nearly preserved in 

 certain Serpents, is recommended by certain general considerations. 



"Whatever may be the views as to the phylogeny of the Squamata., 

 it can hardly be disallowed that Reptiles generally have emerged 

 fi-om an Amphibian or Dipnoan form. On this view, the com- 

 mencement of the lung far forward in the body is intelligible, for 

 the earliest condition known, that represented in the Dipnoi, 

 shows a lung at first (or always, Ceratodus) vinpaired communicating 

 directly with the exterior through the glottis and mouth-cavity. 



* Above p. 36. 



t " On the Anatomy of the Yellow-throated Lizard," P. Z. S. 1904, vol. ii. p. 263, 

 text-fig. 37. 



X " On the Vascular System of Hatteria &c.," P. Z. S. 1905, vol. ii. p. 462. 



