230 



EESPIEATION. 



in the embryo of the sixth day. 

 Both figures twice the size of 

 nature. 



bits a peculiar structure, which may be studied very readily in 



the lungs of the live newt (fig. 

 230), or in preparations of the 

 same part that have been finely 

 injected. From the whole extent 

 of the pulmonary artery a vast 

 number of very small arteries arise, 

 , the orifices of which give the inner 



Fig. 244. a, Rudiment of the surface of its principal branches 

 lung in the embryo of the fowl the appearance of a regularly per- 

 of the fourth day ; b, the lung forated sieve ; these minute ves- 

 sels form a very close irregular 

 hexagonal intermediate net-work, 

 without resolving themselves into 

 branches and twigs like a tree, 

 and so forming a capillary rete. 

 Yet single larger vessels (fig. 

 230, d) proceed from the 

 pulmonary artery to reach some 

 more remote part of the lung. 

 The pulmonary vein, like the pul- 

 monary artery, is partly perforated 

 at every point in its course for the 

 reception of smaller vessels, and 

 is partly formed by larger venous 

 trunks, which collect and bring 



sheep, an inch and a half long, the blood from greater distances 

 seen under the microscope (af- / fi ^ 2 30, c). The islets of the 



A. A/T :i11vM 71 s* ffl nvin G>/*OV*<Y* . ... 



thin and indistinctly cellular pa- 

 renchyma, are often of a di- 

 ameter inferior to that of the ves- 

 sels which surround them ; this 

 is the case in the tortoise, for ex- 

 ample (fig. 239), and appears to 

 be the case in man also (figs. 241, 

 242). It is remarkable that 

 even in the more conspicuous 

 branches of the pulmonary vas- 

 system, the layer of trans- 



Fig. 245. The greater part 

 of the right lung of a fetal 



ter Miiller, De Gland, secern, 

 struct, penit. T. xvii. f. 7). 



Fig 246. Termination of one 

 of the branchings of the bronchi 



from the lung of a very young " Uli " ^ m ^ ia ^ c 

 embryo of the hog after Rathke parent lymph in immediate con- 



Cfig. viii. T. xviii.) 



j- > -*. 



tact with the walls of the vessels 



