6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



arrangement. The outlines of the cells to which the nuclei belong 

 could not be determined. 



Besides this small mass of parathyroid or post-branchial tissue, 

 imbedded in the side of the thyroid gland, there are several small, 

 more or less spheroidal bodies situated on each side of the neck, near, 

 or even imbedded in the thymus glands. They are so small — about 

 the size of an ordinary pin head in a 28-inch alligator — that they are 

 distinguished with difficulty from the surrounding tissue. 



J. B. Looper (7), who first called my attention to them, finds two or 

 three on each side of the neck near, posterior or median to the thy- 

 mus, sometimes imbedded in it and apparently continuous with it. 

 Kingsley (5) does not mention the parathyroid in the alligator, but he 

 figures the pharyngeal derivatives in a lizard and shows a single, 

 rather large parathyroid lying against the trachea, posterior to the 

 thyroid. Vincent (11) does not mention the parathyroid in the croco- 

 diles. He says : 



The parathyroids and post-branchial bodies are intimately united, paired, and 

 placed anteriorly to the thyroid. Their precise anatomy differs in different groups. 

 .... In Chrysemys picta the post-branchial body also contains colloid, but the 

 parathyroid and post-branchial body are very considerably confused together in 

 this and some other species. 



A section of a parathyroid and its adjacent structures from a 

 28-inch alligator is shown in plate 2, figure 8, drawn with a camera 

 lucida under a magnification of about 100 diameters. The gland and 

 adjacent structures are surrounded by a fairly compact capsule (f) 

 of fibrous connective tissue. The capsule sends into the body of the 

 gland many broad trabeculae (t) which are very vascular and break 

 up the gland into numerous lobules or cords of cells. Capillaries (ca) 

 generally filled with blood corpuscles, are seen at many places in the 

 trabeculae and among the cells of the gland. To the right of the 

 gland and inclosed in its capsule is seen an elongated, granular mass 

 which may represent a post-branchial body (pb). 



A portion of the same section, more highly magnified, is shown in 

 figure 9 (pi. 2). Two masses of cells with a broad trabecula (t) 

 between them are seen to the left, and to the right of a broad mass 

 of connective tissue (ct) is a portion of the so-called post-branchial 

 body (pb). 



The gland cells (gc) are closely and irregularly packed together, 

 and even under an oil immersion objective no cell walls could be 

 made out, and in but few cases could any lines of demarkation be- 

 tween the cells be seen. The nuclei are oval or round and are densely 



