430 THE SOLIDS. 



been torn up, others will be observed to be attached to the 

 tubes which take their origin from them. All of these, how- 

 ever, whether attached or loose, will occur in one of two 

 states ; either the surface of each will be seen to be constituted 

 of convoluted and branched tubes, the vessels of the Malpig- 

 hian plexus ; or it will appear perfectly smooth and even. 

 The former condition is the more frequent ; the latter is by 

 far the less common, and is explained by the fact that in this 

 case the Malpighian dilatation is inclosed in a capsule of 

 fibro-elastic tissue of considerable thickness, a continuation of 

 that which invests the tubes themselves. (See Plate LX. 

 figs. 2, 3, and Plate LVIII. fig. 2.) 



The Malpighian dilatations rarely, if ever, extend to the 

 surface of the kidney ; they have been, in all the instances in 

 which they have been noticed by the Author, covered by con- 

 volutions of the tubes. 



Epithelium. The epithelium of the kidney presents several 

 well-marked modifications, in different localities of that organ. 

 The epithelium of the tubes of the cortical part of the 

 kidney, save within a short distance of their junction with the 

 Malpighian dilatations, is composed of large and angular scales 

 or cells, which are coarsely granular, and which form a regular 

 layer of pavement epithelium lining the tubes ; the centres of 

 these are unoccupied with cells, and are thus left pervious for 

 the passage of the urine. (See Plate LVIII. fig. 6.) 



The cells forming the epithelium of the tubes of the me- 

 dullary part of the kidney are of much smaller size than those 

 contained in the tubes of its cortical substance, consisting of 

 nuclei, surrounded by a very narrow border. (See Plate 

 LVIII. fig. 6.) 



The cells situated at the neck of the Malpighian dilatations 

 are of the ciliated kind : these were first noticed by Mr. Bow- 

 man in the kidney of the frog, and that gentleman conjectured 

 their existence in the higher animals ; the Author has seen 

 them in action in the sheep, rabbit, and horse. (See Plate 

 LX. fig. 3.) 



Lastly, the cells which invariably line the Malpighian 

 dilatations of the tubes are small and furnished with oval 



