320 MR TURNER ON THE THYMUS AND 
porpoise (Phoccena communis), one was a foetus, twelve inches long; another was 
a well-grown male, three feet ten inches long; the third being a full grown male, 
between five and six feet in length. 
On removing in each of these animals the large sterno-hyoid and smaller 
sterno-thyroid muscles, a distinct and well-defined glandular mass was seen 
lying on the anterior and lateral surfaces of the trachea at its upper end, and 
extending slightly upwards on each side over the outer surface of the cricoid 
cartilage. Its position thus closely corresponded with that of the thyroid gland in 
other mammalia. Instead, however, of being divided into two distinct lateral 
lobes, as described by Cuvier and Carus, the gland consisted of a single uniform 
mass, which in the adult animal was two inches long, extending across the middle 
line, and closely fitting both to the front and sides of the trachea. The median 
portion of the gland can hardly be described as an intervening isthmus, for in its 
supero-inferior diameter it equalled that of the lateral portion. This, in the 
adult animal, was three-fourths of an inch, in the foetus, one-fourth. 
In the full grown specimen (which was examined in the fresh state, the other 
specimens having been for some time in spirits), the gland presented a dark 
purple tint, and a soft and somewhat succulent aspect. At the upper end of 
each lateral portion, but separated from it by a slight interval, a glandular mass 
about the size of a small nut was found, apparently an accessory thyroid. In 
this respect the gland corresponded in its arrangement to one which is occa- 
sionally found in the human subject. 
In the smaller adult porpoise, in the interval between the two crico-thyroid 
muscles, and almost concealed by the plates of the cricoid cartilage, a small 
glandular mass was situated. It had the same colour as the thyroid; but 
presented more evident indications of being divided into distinct lobes. It was 
in contact by its deep surface with the crico-thyroid membrane. It must, I 
think, be regarded as an isolated portion of the thymus. 
In the foetal porpoise, a long and slender glandular process extended from the 
inferior margin of the median part of the thyroid, downwards along the anterior 
surface of the trachea, and behind the heart and pericardium, into the posterior 
mediastinum. This must also be looked upon as a part of the thymus. 
Both in the foetal and smaller adult porpoise, the thymus gland was exceed- 
ingly well developed. As the thymus closely corresponds in its structure to the _ 
thyroid, and as the relations of the two glands are extremely interesting in a 
developmental point of view, I purpose, in the next place, describing the general 
disposition and arrangement of the thymus in these animals. 
This gland was exposed by cutting through the sterno-hyoid and thyroid muscles, 
and by turning on one side the upper end of the sternum. It was composed of two 
large lateral lobes, separated from each other by a thin layer of cellular tissue. 
These lobes, of a conical form, were situated for the most part behind the first 

