10 The Anatomy of <strong>the</strong> Parathyroid Glands <strong>in</strong> <strong>the</strong> <strong>Horse</strong> ESTES’ (1907) description clearly established that three ma<strong>in</strong> types of epi<strong>the</strong>lial cells occur <strong>in</strong> <strong>the</strong> equ<strong>in</strong>e parathyroid, viz., chief cells, water-clear cells, and oxyphil cells. This should be emphasized <strong>in</strong> view of <strong>the</strong> fact that even modern textbooks and papers deal<strong>in</strong>g with general parathyroid histology stress <strong>the</strong> existence of water-clear cells and oxyphil cells as a characteristic of <strong>the</strong> human parathyroid gland only. LITTY (1907) dist<strong>in</strong>guished two types of epi<strong>the</strong>lial cells <strong>in</strong> <strong>the</strong> equ<strong>in</strong>e parathyroid. In addition to <strong>the</strong> predom<strong>in</strong>at<strong>in</strong>g light chief cells (accord<strong>in</strong>g to modern nomenclature), he described large cells with well-def<strong>in</strong>ed borders, a clear cytoplasm, and a nucleus hav<strong>in</strong>g variable sta<strong>in</strong><strong>in</strong>g properties. These cells usually occurred <strong>in</strong> restricted areas <strong>in</strong> small groups, but <strong>in</strong> rare cases <strong>the</strong>y predom<strong>in</strong>ated <strong>in</strong> <strong>the</strong> microscopic field. BOBEAU (1911) contributed a detailed description of <strong>the</strong> histology of <strong>the</strong> equ<strong>in</strong>e parathyroids. He recognized four epi<strong>the</strong>lial cell types, viz., light chief cells (celldes normales) with a longitud<strong>in</strong>al diameter of 12 to 16 p and a nucleus of 5 to 7 p; water-clear cells (celhles claires) with no sta<strong>in</strong>able cytoplasm (“one has <strong>the</strong> impression of nuclei float<strong>in</strong>g <strong>in</strong> an empty space”); dark oxyphil cells (cellules sombres) with a longitud<strong>in</strong>al diameter of 10 p and deeply eos<strong>in</strong>ophilic cytoplasm; and pale oxyphil cells (grosses celldes ci prod& gramdegx ozt colloid). BOBEAU also exam<strong>in</strong>ed <strong>the</strong> parathyroids for fat. He stated that fat was present <strong>in</strong> <strong>the</strong> cytoplasm of <strong>the</strong> light chief cells and, more rarely, <strong>in</strong> <strong>the</strong> dark oxyphil cells but never <strong>in</strong> <strong>the</strong> water-clear and pale oxyphil cells. Unfortunately, BOBEAU did not give <strong>the</strong> age of any of his horses, and <strong>the</strong> correlation between age and <strong>the</strong> degree of fat present <strong>in</strong> <strong>the</strong> cells is <strong>the</strong>refore lack<strong>in</strong>g. VERMEULEN (1917) described two ma<strong>in</strong> epi<strong>the</strong>lial cell types, viz., chief cells and oxyphil cells. He also proposed a classification of <strong>the</strong> parathyroid glands accord<strong>in</strong>g to <strong>the</strong> amount and arrangement of connective tissue with<strong>in</strong> <strong>the</strong> glands. Fig. 3. Lower parathyroids of horses, both male and 12 years old. Parathyroid at straight arrow, cyst at curved arrows, x 4.5. Fig. 4. <strong>Horse</strong>, female, 22 years old. Relative size of parathyroid glands. Left part of figure: upper gland; right part: lower gland, x 5. Fig. 5. <strong>Horse</strong>, female, 17 years old. Typical structure of parathyroid gland. Th<strong>in</strong> connective tissue septa subdivid<strong>in</strong>g gland <strong>in</strong>to f<strong>in</strong>e lobuli. Rich vascularization. Ma<strong>in</strong>ly light chief cells. H & E, x 275. Fig. 6. <strong>Horse</strong>, male, 1 year old. Relatively abundant stroma <strong>in</strong> parathyroid gland. Numerous KURSTEINER’S canals (straight arrow) and cysts (curved arrows) at hilus. H & E, x 22.5. Downloaded from vet.sagepub.com by guest on April 14, 2010
'I'hc hlicroscopic Anatomy of <strong>the</strong> Equiiic Parathyroid Glands 11 Downloaded from vet.sagepub.com by guest on April 14, 2010