I30 BIOLOGY OF THE LABORATORY MOUSE 



collagenous fibers. Elastic and reticular fibers are present in the inter- 

 alveolar septa. The cells which line the alveolar walls are the so-called 

 "septal cells." They are large flat cells with oval nuclei and are closely 

 attached to the walls of the capillary network. The entodermal or mesen- 

 chymal origin of these cells is still uncertain. The alveolar wall of the mouse 

 contains a varying number of lymphocytes and occasionally granular 

 leukocytes. 



The lungs receive blood from the branches of the pulmonary arteries 

 which follow the course of the bronchi. From these an arteriole passes to 

 each alveolar duct and forms the network of capillaries in the walls of the 

 alveoli. The pulmonary veins are formed by capillaries of the alveolar 

 septa and of the pleura, and follow the course of the bronchi. The smaller 

 bronchial arteries supply arterial blood to the wall of the bronchi and collect 

 into the bronchial veins. The media of the walls of the veins in the lung 

 are composed of cardiac muscle fibers (Fig. 60). 



Urinary System 



The kidney. — The kidney is a compound tubular gland composed of 

 uriniferous tubules enclosed within a thin connective tissue capsule. A 

 rrfedian section through the middle of the kidney shows a division into a 

 cortical part containing mostly convoluted tubules, and a medullary part 

 containing radially arranged straight tubules. The medulla is pyramidal 

 in shape with the broad surface outward, and the apex ending in a single 

 nipple-shaped dorsoventrally flattened papilla (Fig. 61). Columns of 

 straight medullary tubules project part way into the cortex where they form 

 the medullary rays. 



The uriniferous tubules of the mouse are similar in structure to those of 

 man, and for their detailed description the reader is referred to Maximow 

 and Bloom (73). 



It has been reported that in some mice the parietal or capsular epithelium 

 of the capsule of Bowman consists partially or entirely of cuboidal epithelial 

 cells (20, 42). Such capsules appear in greater number in the male than in 

 the female animals (20). 



The circulation of the mouse kidney is similar in general to the circulation 

 in the human kidney (56). In the media of the glomerular arteries, in 

 addition to the ordinary smooth muscle cells, larger, more afibrillar cells are 

 present. These are similar to the cells described by Goormaghtigh (40) 

 who states that they tend to accumulate in groups at the vascular poles of 

 the glomeruli and form the ''juxtaglomerular apparatus" (41). 



