GENERAL STRUCTURE OF THE RESPIRATORY ORGANS. 



507 



ticularly strong and well marked around the apertures of communication between 

 the contiguous air-cells. These fibres have not any resemblance to muscular 

 tissue; but rather correspond with those of yellow fibrous tissue. 1 The diame- 



Fig. 144. 



The Larynx, Trachea, and Bronchise, deprived of their fibrous covering, and with the outline of the Lungs : 

 1, 1, outline of the upper lobes of the lungs; 2, outline of the middle lobe of the right lung ; 3, 3, outline of 

 the inferior lobes of both lungs ; 4, outline of the ninth dorsal vertebra, showing its relation to the lungs and 

 the vertebral column; 5, thyroid cartilage; 6, cricoid cartilage; 7, trachea; 8, right bronchus; 9, left bron- 

 chus; 10, crico-thyroid ligament; 11, 12, rings of the trachea; 13, first ring of the trachea; 14, last ring of 

 the trachea, which is corset-shaped; 15, 16, a complete bronchial cartilaginous ring; 17, one which is bifur- 

 cated ; 18, double bifurcated bronchial rings ; 19, 19, smaller bronchial rings ; 20, depressions for the course 

 of the large bloodvessels. 



ter of the Human air-cells is about twenty times greater than that of the capil- 

 laries which are distributed upon their parietes ; varying (according to the 

 measurement of Weber) from the l-200th to the l-70th of an inch. 2 It has 

 been calculated by M. Rouchoux, that as many as 17,790 air-cells are grouped 

 around each terminal bronchus ; and that their total number amounts to no less 

 than 600 millions. The capillary plexus is so disposed between the two layers 

 which form the walls of two adjacent air-cells, as to expose one of its surfaces to 



1 It is suspected by Kolliker that there may be muscular fibre-cells among these, as he 

 sees long nuclei in the walls of the air-vesicles. These, however, are neither so long nor 

 so narrow as the proper nuclei of the fibre-cells (Fig. 22), and are just as probably the 

 nuclei of capillary bloodvessels (Fig. 88). 



2 The dimensions given by Moleschott ("De Vesiculis Pulmonum Malpighianis") are 

 very much less than these ; the range of diameter being stated by him at between 1-1 20th 

 and l-1200th of an inch. The Author's own observations, however, lead him to regard 

 Weber's statement as very near the truth; and that of Prof. Kolliker (" Mikroskopische 

 Anatomie," band. ii. 196) is almost precisely the same. 



