206 MICROSCOPIC ANATOMY OF THE 



liver it is so scarce that one cannot distinguish it as a separate 

 layer, and the serosa seems to be a part of the organ upon 

 which it lies. 



The blood supply of the peritoneum is made up of an 

 extensive capillary network. The lymph-vessels can be seen 

 especially well in the mesentery of an animal which has 

 recently had a fatty meal. Here they stand out as a white net- 

 work of anastomosing vessels. The nerves are non-medullated, 

 and end either freely or in the form of Pacinian corpuscles 

 (see Nerve-endings). 



III. RESPIRATORY SYSTEM. 

 A. LARYNX AND TRACHEA. 



The mucous membrane of the larynx, like that of the tra- 

 chea, consists of a ciliated epithelium, whose cilia move in the 

 direction of the pharyngeal cavity. In the true vocal cords 

 and on the posterior surface of the epiglottis is found a strati- 

 fied pavement epithelium. In these places the tunica propria 

 forms no papilla. 



The tunica propria is a connective-tissue sheath, containing 

 elastic fibres and leucocytes, which vary in quantity in different 

 places. Solitary follicles are not often seen. At the border of 

 the epithelial cells is a basement membrane (membrana propria). 

 This represents a thickening of the subepithelial connective 

 tissue. In the tunica propria there are many smooth muscle 

 cells, which in the posterior part of the tracheal wall are 

 strongly developed and join together the ends of the C-shaped 

 cartilage rings. The submucosa contains a number of branched 

 tubular mucous glands, which are largest in the posterior wall 

 of the trachea, and here often penetrate into the muscle layer. 



The cartilaginous framework of the larynx and trachea is 

 made up of hyaline cartilage, with the exception of the carti- 

 lage of Wrisberg arid Santorini, and the median part of the 

 thyroid cartilage, which are made up of elastic cartilage. 



The blood- and lymph-vessels form wide networks parallel 

 to the surface. The nerves show small ganglia in their course, 



