448 MANUAL OF HISTOLOGY. 



endothelium, are regarded now as covering vessels situated in its in- 

 terior. 



The so-called ganglion inter car oticum, which was found by Lusdika to 

 be very similar, as regards its microscopical appearance, to the coccygeal 

 gland, has also been declared by Arnold to have the same peculiar vascular 

 structure as the latter. 



2. Respiratory Apparatus. 



239. 



The respiratory apparatus is made up of a system of branching canals 

 for the entrance and exit of air, and a proper respiratory part. The first 

 of these is represented by the larynx trachea and its ramifications, the 

 latter by the lungs. The whole may be compared to a racemose gland. 

 It presents important peculiarities as well physiologically as anatomically, 

 and especially in the high development of its elastic tissue. 



The larynx consists, we know from descriptive anatomy, of several 

 cartilages, the ligaments connecting these one with another, the muscles 

 by which they are moved, and a lining of mucous membrane. 



In describing cartilaginous tissue we have already referred to the 

 various cartilages of the larynx. These afford examples of the different 

 species of this tissue. The thyroid, crycoid, and arytenoid are formed of 

 hyaline substance. At certain points in the latter, however, namely, in 

 the processus vocalis and apex, a change into elastic cartilaginous tissue 

 has already commenced ( 107, p. 176). The cartilages of Wrisberg and 

 Santorini, and the epiglottis, are entirely formed of the latter tissue ( 108, 

 p. 180), while the c. triticea appear to be principally composed of iibrous 

 tissue ( 109, p. 181). 



The ligaments of the larynx are either almost entirely composed of 

 elastic fibres, or are at least very rich in them (p. 229). Those in which 

 the essentially elastic nature is best marked are the vocal cords, the 

 ligamenta tltyreo-arytcenoidea inferiora. 



The muscles of the larynx belong to the striped class ( 164, p. 103). 



The epiglottis is in the human subject covered on its anterior surface 

 with a strongly laminated epithelium - 2 or 0'3 mm. in depth, and on 

 its posterior aspect with a much thinner bed, only - 06 or O'l mm. The 

 lower part of the latter is lined with laminated ciliary epithelium 0'15 

 mm. or even more in thickness. 



The mucous membrane, which, especially in its deeper portions, is rich 

 in elastic tissue, presents as a rule a smooth surface and tough texture. 



At certain points, however, it presents larger or smaller papillae, as on 

 the true vocal cords. Its most superficial layer contains lymph cor- 

 puscles embedded in it close under the epithelium. These may be pre- 

 sent in such number as to give rise to regular lymphoid follicles, single or 

 grouped. 



Finally, it is studded with numerous racemose mucous glands, either 

 scattered or crowded together in certain situations. The bodies of these 

 glands may lie embedded in depressions in the subjacent cartilage. It is 

 by these organs that the mucus of the larynx is secreted. Their excretory 

 canal appears thick-walled, and the acini are frequently elongated and 

 clothed with low columnar cells. 



From the base of the epiglottis and false vocal cords the epithelium 

 (with the exception of that clothing the true cords, which is of the 



