Abstract: This work aims to study the anatomical structure of the yak kidney collection system. Twenty-four collecting system casting specimens, which were made by ABS (acrylonitrile butadiene styrene), were observed to study its anatomical structure. The results showed that the renal pelvis was present in all casts and is classified into 2 types, dilated or nondilated (58.3%), with or without the dilated origin of the ureter. All casts had 2 major renal calyces toward the cranial and the caudal poles. Minor renal calyces were connected to the major renal calyces by an infundibulum, which drained 1 to 5 minor renal calyces. The number of minor renal calyces in the caudal region was significantly more than that in cranial (P<0.01). The yak kidney collection system was classified into 2 types according to the character of drainage. The type A, which was composed of the collection system that presented two major caliceal groups and mid-zone drainage was dependent on these major groups, and type B, which mid-zone drainage was independent of the polar caliceal groups, the type A (70.8%) was more common than type B (29.2%) in the yak. The collection system of yak kidney was composed of 1 renal pelvis, 2 major renal calyces, and multiple (11-21) minor renal calyces. According to the characteristics of drainage, it was divided into 2 types, A and B, of which type A is more common.

Key words: yak, renal collection system, cast