1906.] RESPIEATORT SYSTEMS IN THE OPHIDIA. 525 



itself, but certain, of the alveoli (about two I think) of the latter 

 are deeper than the rest and communicate with the pulmonary 

 appendage. In a transverse section of the latter it is seen to be 

 for the most part solid, with a cavity at either side. It seems to 

 be a prolongation of the outer edge of the lung proper, which is 

 thicker in its wall than the rest of the lung. There is no special 

 communication of the headward extension of the lung with the 

 trachea. The lung ceases to be vascular some way doAvn the 

 liver, and ends altogether a few inches before the termination 

 posteriorly of the liver. 



When the trachea of Erythrolaniprus (text-fig. 93, p. 526) is cut 

 open, it is seen that, as in many (probably in all) Snakes, the tube 

 is not completely encircled with the cartilaginous hoops. There 

 is a median dorsal area Avhich is occupied by soft tissue. This 

 area of soft tissue is continuous with the lung-tissue, and, more 

 than that, it is not merely a fibrous membrane but is divided into 

 hexagonal cells. It presents, in fact, the honeycombed appearance 

 of the lung though less marked. This is obviously a tracheal 

 lung, recorded in this Serpent here for the first time, so far as I 

 am aware. The tracheal lung of Erythrolamjirus is, however, of 

 small dimensions. The cells are ranged not more than two or 

 three deep. The lung therefore does not project doi'saUy from 

 the trachea as in the better-developed forms of tracheal lung. It 

 is not, in fact, wider than in many forms where there is no deve- 

 lopment of pulmonary tissue in this region, but merely a fibrous 

 connecting-band between the tracheal semirings. The tracheal 

 lung, however, inextensive as it is, seems to function as a lung, 

 for it is vascvilar and of the same red colour as the functional 

 lung below. It has, moreover, a special branch of the pulmonary 

 artery supplying it. The pulmonary artery of this Snake is single 

 (text-fig. 93). It reaches the lung at the apex of the anterior lobe, 

 and passes obliquely back, lying ultimately to the outside of the 

 lung outside of the vena cava inferior, which covers in the natural 

 position of the viscera the pulmonary vein. The artery before it 

 quite reaches the lung gives off a branch which at once divides 

 into two. The lower of these branches supplies the anterior 

 lobe of the lung. The upper branch turns back, and runs up the 

 trachea along the pulmonaiy surface of that tube. It corresponds 

 therefore to the anterior branch of the pulmonaiy artery in 

 Bitis *, and to the tracheal branch of the pulmonary artery in 

 certain Lizards f. The pulmonary artery can be traced nearly to 

 the end of the lung ; it is to be seen in the posterior anangious 

 region of that viscus. At regular intervals it gives oflf branches 

 running across the lung. In the anangious region these branches 

 are slender ; it is an interesting fact that they end by anasto- 

 mosing with the intercostals above. The nutritive blood of the 

 lung is therefore not separated frora the respiratory blood. 



* Beddard, " Contributions to the Anatomy of the Ophidia," P. Z. S. 1906, vol. i. 

 p. 36. 



t Id. ihid. p. 44. , 



