The kidney of tapirs: a macroscopical study

The renal cortex of tapirs, water-loving primordial ungulates, was continuous, nonlobed, and about 80% of renal mass in adult and 71% in term-neonate. In the neonates even the peripheral glomeruli were moderately mature. Tapirus bairdi had about 4 million glomeruli per kidney and T. pinchaque about 3 million smaller glomeruli. Number of glomeruli per gm of cortex was 12,444 in T. bairdi and 13,400 in T. pinchaque. Cortical loops were common in the medullary rays. The medulla was the simple crest-type. The terminal collecting ducts (T.C.D.) opened separately at the crest and not into a tubus maximus. The "outer stripe" of the outer medulla apparently was telescoped into the deep cortex. The medullary loops turned at a thick portion and at nearly all levels of the medulla. The medullary crest was lined by urothelium which extended into the ends of the T.C.D. Otherwise the T.C.D. were made of columnar epithelium. The pelvic urothelium was continuous with that of the medullary crest at the dorsal and ventral fornices. The fornices were well within the inner medulla. Hence only inner medulla could be exposed to pelvic urine. The hilar arteries, unlike the other two perissodactyl families (rhinoceri and equids), passed through the cortico-medullary (C-M) border and some large arteries and veins passed through the outer medulla to and from the C-M border without branches or tributaries. Unlike kidneys with a medullary crest in diverse eutherian mammals, tapirs lacked pelvic extensions along the major intrarenal blood vessels and thus lacked pelvic intervascular eminences.