THE EVIDENCE OF THE THYROID GLAND 195 
chamber, and is curled upon itself in its more posterior part. This 
central chamber divides, anteriorly to the thyroid orifice, into two 
portions, A, A’ (Fig. 82), giving origin to two tubes, B, B’, which lie 
close alongside of, and extend further back than, the posterior limit 
of the curled portion of the central chamber, C. The structure of 
the central chamber, C, and, therefore, of the separate coils, is given 
in both Schneider's and Dohrn’s pictures, and is represented in 
Fig. 81 (6), which shows the peculiar arrangement and character of 
the glandular cells typical of this organ, and also the nature of the 
central cavity, with the arrangement of the ciliated epithelium. The 
structure of each of the lateral tubes, B, is different from that of the 
central chamber, in that only half the central chamber is present 
in them, as is seen by the comparison of the tube B with the tube C 
in Fig. 81 (5 and 6), so that we may look upon the central chamber, 
C, as formed of two tubes, similar in structure to the tubes B, which 
have come together to form a single chamber by the partial absorp- 
tion of their walls, the remains of the wall being still visible as the 
septum, which partially divides the chamber, C, into halves. 
In the walls of each of these tubes is situated a continuous 
glandular line, the structure of the glandular elements being specially 
characterized by the length of the cells, by the large spherical nucleus 
situated at the very base of each cell, and by the way in which the 
cells form a wedge-shaped group, the thin points of all the wedge- 
shaped cells coming together so as to form a continuous_line along 
the chamber wall. This free termination of the cells of the gland 
in the lumen of the chamber constitutes the whole method for the 
secretion of the gland; there is no duct, no alveolus, nothing but this 
free termination of the cells. 
Moreover, sections through the portion A, A’ (Fig. 82) show that 
here, as in the central chamber, C, four of these glandular lines open 
into a common chamber, but they are not the same four as in the case 
of the central chamber, for if we name these glandular lines on the left 
side a b, a’ b' (Fig. 81), and on the right side ¢ d, ¢' d’, then the central 
chamber has opening into it the glands a 0,¢ d, while the chambers of 
A and A’ have opening into them respectively a 0, a’ 0’, and ed,’ d’. 
’ Further, the same series of sections shows that the glands a and 6 are 
continuous with the glands a’ and 0’ respectively across the apex of A, 
and similarly on the other side, so that the two glandular rows a b 
are continuous with the two glandular rows a’ 0’, and we see that the 
