648 



This plexus in the larger tubes is reinforced by blood-vessels derived 

 from numerous leaflets which surround the bronchial tubes ; straight 

 vessels penetrate from these leaflets through the walls of the bronchial 

 tubes, to reach the plexus in the mucous membrane. 



On the external surface of the bronchial tubes, numerous radiating 

 vessels collect the blood from the plexus in the mucous membrane, 

 and the trunks of these radiating vessels soon terminate in the veins, 

 already described as coming into contact with the under surface of 

 the bronchial tube. 



The vessels which have been alluded to as receiving their tri- 

 butaries in the interlobular surfaces, collect their blood from all the 

 surrounding lobules ; consequently the blood which reaches the vein 

 placed in contact with a particular bronchial tube, is not derived 

 exclusively from the same lobules as those with which that bronchial 

 tube and its accompanying artery are in connexion, but it receives 

 its blood from all parts of the lungs promiscuously. 



The pulmonary veins accompanying the bronchial tubes continue 

 to increase in size in proportion as the tubes themselves increase, and 

 finally they terminate in the large veins which enter the left auricle. 



XVII. " On the Curvature of the Indian Arc." By the Vene- 

 rable J. H. PRATT, Archdeacon of Calcutta. Communicated 

 by Prof. STOKES, Sec. U.S. Received Sept. 3, I860. 

 (Abstract.) 



This communication completes the series of the author's papers 

 on the subject of the Indian Arc. He commences by recapitulating 

 the chief results of his former calculations, and adverting to the at- 

 tempt which he made in his former papers to explain the difficulty 

 which those calculations brought to light, namely, that the ampli- 

 tudes of the arcs from Kaliana to Kalianpur and from Kalianpur to 

 Damargida, determined geodetically, were so little in excess as they 

 proved to be of the same amplitudes determined astronomically, a 

 difficulty which he endeavoured to get over by attributing to the 

 Indian Arc a curvature different from that corresponding to the mean 

 meridian of the earth. In the present communication, introducing 

 the condition that the length of the chord of the arc must be the same 

 in both the ellipses, the local and the mean, drawn through the 



