418 DISCOVERY REPORTS 



these pairs grow in size, however, the elongation of their tubules may possibly cause 

 some measure of growth apart from one another of the two members of the pair. 



There is no correlation whatever between the size of the kidney, or the size of the 

 individual renculi of which it is made up, and the number of paired renculi in a random 

 sample. Such a correlation, however, can hardly be expected, since the causes governing 

 the growth of the renculi must be very diverse and must include a great variety of factors, 

 such as the amount of space available among surrounding renculi and the position 

 within the kidney with regard to the arterial supply, so that some renculi will grow 

 faster than others and attain a larger size. 



In spite of the many irregularities which exist in the structure of the kidney, it is 

 possible to discern a definite basic architecture underlying the apparently random 

 distribution of the renculi. All kidneys, both adult and foetal, are fairly definitely 

 divided into a dorsal and a ventral half by a horizontal core of connective tissue 

 (Figs. 23 d, 24 d, 25 d, 26 c), forming a fibrous plane lying in the centre of the kidney. The 

 central core is in communication with the serosa and the capsula fibrosa along a slit, as 

 mentioned before, in the mesal face of the kidney. This slit — the mesal slit (Figs. 23 c, 

 24 c, 25 c) — runs from the point of entrance of the blood vessels anteriorly to the point 

 of emergence of the ureter behind. It corresponds to the hilus in a non-lobulated kidney. 

 In these two extreme positions the slit is wide; but it narrows down considerably 

 between them in the middle of its length, so that its opposite sides nearly meet. The 

 actual kidney substance is thus crescentic in section (Figs. 23, 24, 25), the centre of the 

 crescent being occupied by the central core which is continuous with the outer invest- 

 ments between the arms of the crescent. Anterior to the blood vessels there is no mesal 

 slit. 



At a variable number of points on the circumference of the transverse section of the 

 organ, fibrous septa run inwards from the outer sheath to the inner core. Their number 

 and position are variable but they are always present, dividing the kidney substance in 

 any given transverse or longitudinal section into a number of lobes (Figs. 23, 24, 25, 26), 

 some six or seven as a rule in transverse section. The lobes of the kidney are pyramidal 

 in shape with their bases turned outwards upon the surface of the organ and their apices 

 directed towards the central core. In longitudinal section (Fig. 26) they present the 

 same triangular shape as in transverse section. The fibrous septa between the lobes — 

 interlobar septa (Figs. 24, 25, 26) — are thus domes of connective tissue with their apices 

 directed centripetally and their bases centrifugally. They carry the main primary urinary 

 ducts from the renculi (Fig. 31) and the main afferent and efferent blood vessels. The 

 lobes themselves are smaller and more numerous close to the horizontal plane of the 

 kidney, and larger and more diffuse on the dorsal and ventral aspects. The main urinary 

 duct and the main blood vessels supplying the lobes lie in the central core (Fig. 32). 



In the youngest kidney examined (18-5 cm., B. musculus) the lobes were distinctly 

 discernible, divided by interlobar septa (Fig. 23 a). The peripheries of the lobes, how- 

 ever, show signs of division into subsidiary lobules by fibrous laminae running inwards 

 between the capsules and tubules (Fig. 23 b). These are the interlobular septa. At this 



