426 



THE BLADDER. 



covered with a Btratified epithelium, wliich is composed of tliree layers 

 of cells. Of these, those forming the middle layer are pyriform (fig. 

 308, b), the upper end being rounded ; whilst the lower end of each cell 

 is prolonged down to the corium, between small, rounded or irregular cells 

 forming the lowermost layer. The cells of the superficial stratum {a) 

 are large and flattened (more so in some animals than in man), cover- 

 ing one, two, or more of the pyriform cells, over which their lower 

 surface is as it were moulded, presenting well-marked depressions (^vith 



Fi?. 308 





Fig. 308. — Epithelial Cki^ls fkom Bladder of Rabbit. About 500 diameters. 



(Klein.) 

 a, large flattened cell from the superficial layer, with two nuclei, and with strongly 

 marked ridges and intervening depressions on its under surface ; h, pear-shaped cells 

 from the second layer ; c, showing the manner in which the pyriform cells are adapted 

 to the dei^ressions of the superficial cells. 



intervening ridges), into which the rounded ends of the pyriform cells 

 fit {c). These large flattened cells have frequently more than one 

 nucleus. There are no villi upon the vesical mucous membrane, but it 

 is provided with minute recesses and with small racemose glands lined 

 with columnar epithelium, which are most abundant in the vicinity of 

 the neck of the bladder. 



Vessels. — The xiqwrior ir/tiral arfrrict proceed from the remaining' pei-vious 

 poi-tions of the hypogastric arteries ; in the adult they appear as direct branches 

 of the internal iliac. Tlie i/ifcrio?- vesical arteries are usually derived from the 

 anterior division of the internal iliac. In the female the uterine arteries also 

 send branches to the bladder. The neck and base of the organ appear to be the 

 most vascular portions. The iri/is form large plexuses around the neck, sides, 

 and base of the bladder ; they eventually pass into the internal iliac veins. The 

 hjinphatics follow a similar course. 



The nerves are derived partly from the hypogastric plexus of the sympathetic, 

 and partly from the sacral plexus of the cerebro-spinal system. The foi-mer are 



