322 MR TURNER ON THE THYMUS AND 
parative anatomy of the thymus, I find that he gives an account of a dissection of 
this gland, which he made in a foetal dolphin. He describes in this cetacean a 
pericardiac portion of the gland, from which long ascending processes proceed, 
which extend upwards in close contiguity with the vertebree, as high as the level 
of the upper part of the trachea, and then bending inwards in front of that tube, 
so as to join in the middle line. The figure which he appends, illustrating this 
description, closely corresponds with the appearances I have seen both in the foetal 
porpoise and in the smaller well-grown animal. I cannot, however, agree with Mr 
SIMON in considering this median tracheal portion as forming a part of the thymus. 
I am disposed to regard it as the thyroid, and as such I have described it in the 
former part of this paper. My reasons for doing so are the following :—It is situ- 
ated exactly in the position of the thyroid gland; it possesses a perfect continuity 
of gland-structure from side to side, so that it does not present the same subdivision 
into lobes which is characteristic of the thymus; its capsule is much more adherent 
than that of the thymus, and it can be separated from the ascending processes of 
the pericardiac portion of the thymus by carefully removing the thin layer of 
cellular tissue which connects it with them. Moreover, there is no other structure, 
either on the front or sides of the trachea and larynx, which can be looked upon 
as constituting a thyroid gland in these mammalia, if this is not regarded as 
such.* 
The persistence of the thymus gland in an animal so well grown as this por- 
poise is a fact of considerable interest, especially if we take into consideration its 
large size. That it was in a condition perfectly capable of performing its func- 
tions, and not merely a collection of fat-cells, as is generally the case where the 
gland in the human subject apparently persists for some years after birth, I was 
enabled to prove by a microscopic examination. On submitting a portion of the 
gland to a magnifying power of 200 diameters, I found it to consist of lobularly 
arranged masses of small closely-packed corpuscles, about the size of, and a 
little larger than, the red corpuscles of the human blood, presenting, in fact, a 
structure exactly similar to that with which we are familiar in the foetal gland. 
We are furnished by this illustration with additional evidence of the fact, so 
especially insisted on by Havesrep and Sron, that the thymus gland is not 
merely a foetal structure, but that it plays an important part in, the animal 
economy for some time after birth. As I had an opportunity of comparing it at 
the same time with the gland in the foetal porpoise, there could be no doubt that 
it had grown considerably after birth, and apparently in a ratio closely corre- 
sponding with that of the growth of the animal. 
* Since this paper was read to the Society, I have dissected the neck of a fetal Dolphin, pro- 
bably the young of a bottle-nose (D. Tursio). This dissection confirms the opinion I had arrived at 
and stated in the text, viz., that the glandular structure in front of the upper part of the trachea in 
the genus Delphinus is the thyroid, and not merely a part of the thymus. 

