DR. H. WATNEY ON - THE MINUTE ANATOMY OE THE THYMUS. 1087 
indications of the cells having a surrounding zone of clear protoplasm, for the nuclei 
are seen outside the granular mass; hut in Plate 88, figs. 36 and 38, the granular 
masses are nucleated and constitute the whole cell. There is some resemblance 
between these granular cells attached to newly-formed connective-tissue, and osteo¬ 
blasts attached to the edge of newly-forming bone ; and this resemblance is not a 
deceptive one, for the granular cells are concerned in forming fibrous tissue, their 
processes are often seen to be fibrillated (see Plate 88, fig. 36), and the fibrillte are 
continuous with those of the connective-tissue trabecula} (see Plate 93, fig. 82). Some¬ 
times the whole cell is directly transformed into fibrillated connective-tissue. * 
The granular cells form blood vessels. They stretch across from vessel to vessel, 
forming bands of granular tissue. In most cases these slender bands of tissue become 
fibrous-tissue. To demonstrate the formation of new vessels, it is therefore necessary 
to select those granular bands stretching between the vessels, where one part of the 
band, or newly-forming vessel, is hollow, and the other part is still formed of a granular 
cell (see Plate 94, fig. 94) or of granular cells (see Plate 94, fig. 93). In the former 
case the vessel is intra-epithelial, and in the latter it is inter-epithelial. 
Prom what do the granular cells arise ? Their position near the blood vessels, their 
being massed in the medulla of the follicle, where at times extravasations take place, 
might suggest the idea that they arise from extravasated colourless blood corpuscles. 
However, that is not the case ; and the figures given in the plates show that they arise 
from the connective-tissue-corpuscles. In Plate 89, fig. 45 B, some of the cells are 
epithelioid connective-tissue-corpuscles, others contain a granular mass in the centre of 
the cell. This transition of epithelioid connective-tissue-corpuscles to granular cells 
can also be seen in Plate 89, figs. 45 A and C (see also figs. 41 and 45 A, g), where 
there is a very small granular mass in an epithelioid cell. The same thing is shown by 
the series of figs. 44 A to F, in which various epithelioid cells are seen with larger or 
smaller granular masses in their interior. An argument might, however, be put forth, 
that the drawings would be equally explained by supposing that the granular cells are 
the first formed, and that they are afterwards transformed into epithelioid cells. This 
argument is answered very completely by the thymus of the Bird, where we find very 
many epithelioid, and very few granular cells (see Plate 95, figs. 100 and 101). The 
thymus of the Tortoise also contains many epithelioid, and very few granular cells. 
Another origin of the granular cells which might be suggested would be either the 
giant cells or the concentric corpuscles. But there are two fatal objections to the view 
that either of these is the forerunner of the granular cells: first, that sometimes in 
the inner edge of the cortex solitary granular cells are seen (see Plate 89, fig. 39), and 
such solitary cells could not have arisen from either of these sources; secondly, that the 
granular cells are found in much greater number than would be the case if they took 
their origin from either the concentric corpuscles or the giant cells. Again, the granular 
* The papers of Zieglek (89) and Telemanns (90), who described the formation of fibrons tissue in 
pathological new formations, by an exactly similar process, will be referred to afterwards. 
MDCCCLXXXII. 6 Z 
