82 PRACTICAL HISTOLOGY. 



branched cells, and study the concentric corpuscles. The reticulum is best seen in prepara- 

 tions mounted in Farrant's solution or glycerine. 



The concentric corpuscles can easily be isolated by teasing a small part of a fresh gland 

 in salt solution. 



THE DUCTLESS GLANDS. 



These are the thyroid gland, hypophysis cerebri,the coccygealand carotid glands of Luschka, 

 and the supra-renal body. They have no special ducts, and their secretions are probably re- 

 moved by the lymphatics. 



THE THYROID GLAND. 



It consists of a capsule and a connective-tissue framework, which subdivides the glands 

 into lobes and lobules. Each lobule is made up of a larger or smaller number of gland-alveoli 

 or gland-vesicles, which are closed sacs of various sizes, and are spherical, oval, or irregular in 

 shape. Each sac or alveolus consists of a membrana propria lined by a single layer of more 

 or less columnar nucleated cells. The size of the central lumen depends essentially on the 

 amount of secretion. These sacs are filled with a transparent, albuminous, viscid, slightly 

 yellow-coloured fluid. It is the accumulation of this fluid, and the consequent distension of 

 these sacs, which constitutes goitre. Not unfrequently the alveoli contain large numbers of 

 coloured blood-corpuscles (Baber). Each alveolus is surrounded by a rich plexus of capillaries 

 which do not penetrate the membrana propria. As in other glands, the large blood-vessels, 

 lymphatics, and nerves lie in the interlobular connective tissue. 



PREPARATION. Harden the thyroid of a child in Mtiller's fluid for three weeks, or in 

 chromic acid and spirit mixture for two weeks. Then transfer it to spirit. Make sections, 

 stain them with logwood, and mount them in dammar. 



EXAMINATION (L). Observe the interlobular connective tissue and the gland-vesicles, 

 which are of different sizes and lined by a single layer of columnar epithelium. (H). 

 Study the membrana propria and epithelium of the gland-vesicles (PI. XVIII., Fig. 4). 



Blood-vessels of the Thyroid. They are easily injected when the whole body of a child or 

 young animal is injected, but the blood-vessels are usually so filled naturally with blood that 

 an injection need not be made. Mount sections stained or unstained in dammar. 



THE SUPRA-RENAL CAPSULES. 



The framework consists of a fibrous tissue capsule, which sends trabecula? into the 

 interior of the organ, which is divided into a cortex and a medulla. In the outermost zone of 

 the cortex the trabeculae form a plexus with polygonal meshes, whilst in the middle zone 

 they are thinner and have a longitudinal arrangement, i.e. radiate inwards ; in the innermost 

 zone of the cortex they again form a polygonal mesh work. A similar plexus of trabeculae 

 exists in the medulla. These meshes are filled with the parenchyma or gland-substance, which 

 varies in appearance in the different zones. In the outer cortical zone they are nucleated, 

 granular, polyhedral cells ; in the middle zone transparent nucleated cells, often containing 

 oil-globules, and arranged in the form of cylinders, which anastomose with each other ; whilst 

 in the inner cortical zone the cells frequently contain a yellowish-brown pigment. With these 



