982 



THE ORGANS OF VOICE AND RESPIRATION. 



Structure. Each lateral lobe is composed of numerous lobules held together 

 by delicate areolar tissue, the entire gland being enclosed in an investing capsule 

 of a similar but denser structure. The primary lobules vary in size from a pin's 

 head to a small pea, and are made up of a number of small nodules or follicles 

 which are irregular in shape and are more or less fused together, especially 

 toward the interior of the gland. Each follicle consists of a medullary and corti- 

 cal portion, which differ in many essential particulars from each other. The corti- 

 cal portion is mainly composed of lymphoid cells supported by a delicate reticulum. 

 In addition to this reticulum, of which traces only are found in the medullary 

 portion, there is also a network of finely branched cells which is continuous with a 

 similar network in the medullary portion. This network forms an adventitia to 

 the blood-vessels. In the medullary portion there are but few lymphoid cells, but 

 there are, especially toward the centre, granular cells arid concentric corpuscles. 

 The granular cells are rounded or flask-shaped masses attached (often by fibril- 

 lated extremities) to blood-vessels and to newly formed connective tissue. The 

 concentric corpuscles are composed of a central mass consisting of one or more 

 granular cells, and of a capsule which is formed of epithelioid cells which are 

 continuous with the branched cells forming the network mentioned above. 



Each follicle is surrounded by a capillary plexus from which vessels pass into 

 the interior and radiate from the periphery toward the centre, and form a second 

 zone just within the margin of the medullary portion. In the centre of the 

 medulla there are very few vessels, and they are of minute size. 



Watney has recently made the important observation that haemoglobin is 

 found in the thymus either in cysts or in cells situated near to or forming part 



FIG. 541. -Minute structure of thymus gland. Upper portion of the thymus of a foetal pig of 2" in 

 length, showing the bud-like lobuli and glandular elements. 2. Cells of the thymus, mostly from a man. 

 a. Free nuclei, b, Srnall p.piis < T,nro-nr /7 i.un>p with r>ii.-in>>iiir *--- -* ~ , . , 



filled with fat; at/wi , 



posite structure of a similar nature. 



o , -ijc uuu-ii*.e j 11 anu gitumiuar eieinenis. z. ueiis 01 tne tnymus, mostly irom a man. 



a. Iree nuclei. 6. Small cells, c. Larger, d. Larger, with oil-globules, from the ox. e, J. Cells completely 

 without a nucleus, g, h. Concentric bodies, g. An encapsulated nucleated cell. h. A com- 



J*. KiTnilwr rintnrti 



of the concentric corpuscles. This haemoglobin varies from granules to masses 

 exactly resembling colored blood-corpuscles, oval in the bird, reptile, and fish ; 

 circular in all mammals except in the camel. Dr. Watney has also discovered 

 in the lymph issuing from the thymus similar cells to those found in the gland, 

 and, like them, containing haemoglobin either in the form of granules or masses. 

 From these facts he arrives at the physiological conclusion that the thymus is one 

 source of the colored blood-corpuscles. 



Vessels and Nerves. The arteries supplying the thymus are derived from 

 the internal mammary and from the superior and inferior thyroid. The veins 

 terminate in the left innominate vein and in the thyroid veins. The lymphatics 



