Cervical Region 
cylindrical tube extending from the larynx at the 
level of the cervical vertebra to the sixth rib where 
it divides into a smaller left and larger right main 
bronchus. The trachea in situ (Fig. 3-20) is 33. 7± 
2.9 mm long in the adult hamster. Isolated, the 
organ has an average length of 23.0±4.3 mm and 
weighs about 86 mg in adult males and 68 mg in 
adult females (Tables 1, 5). 
The ventral surface of the cervical trachea is 
covered by the sternohyoid muscle, which also over- 
laps the thymus, thyroid and parathyroid glands; 
the caudal thyroid veins; cervical fascia and, super- 
ficially, the anastomosing branches of the jugular 
veins. The lateral surface is related to the common 
carotid arteries, the right and left lobes of the thy- 
roid gland, the caudal thyroid arteries and the 
recurrent laryngeal nerves. The cervical trachea 
lies ventral to the esophagus in the dorsal part of 
the neck (Fig. 3-16). It is accompanied on both 
sides by the common carotid arteries. 
The skeleton of the trachea consists of 14 or 15 
hyaline cartilaginous rings (Figs. 3-12, 3-15, 3- 
16) (Reznik, et ai, 1973). The first tracheal ring, 
3.9 mm in luminal diameter, is the largest while the 
last tracheal ring, with a lumen diameter of 2.7 mm, 
is the smallest (Table 1). All of the rings are ap- 
proximately 0.5 mm thick, even though their lumi- 
nal diameters vary (Figs. 3-15, 3-17, Table 1). The 
tracheal cartilages {cartilagines tracheales) are 
slightly compressed; the c-shaped rings are incom- 
plete dorsally (Fig. 3-16). The first tracheal ring 
is joined to the cricoid cartilage by the cricotracheal 
ligament, while annular ligaments {ligg- annularia) 
connect all tracheal rings in series. Very thin trans- 
verse muscle fibers {mm. tracheales) connect the 
two open ends of each ring on the dorsal aspect of 
the tube. 
The tracheal lumen is lined by pseudostratified ciliated columnar 
epithelium, with only a few submucosal glands interspersed, especially 
cranially; some isolated seromucous glands are found in the adventitia 
(Fig. 3-21). 
3.7 THYROID AND PARATHYROID 
GLAND 
The thyroid {gl. thyreoidea) and parathyroid 
glands {gl. parathyreoidea) belong to the endocrine 
hormonal system and supply the body with thyroxin 
and parathormone. In contrast to the findings of 
other workers (Kittel, 1952-53), the gland lies lat- 
eral and dorsal to the trachea between the caudal 
plate of the thyroid cartilage and the first three 
tracheal rings (Fig. 3-14). This highly vascular 
gland is larger in hibernating than in non-hibernat- 
ing animals. In hibernating animals it weighs 
around 10 mg (Kittel, 1952-53) and consists of two 
longitudinally oval glandular bodies which can be 
up to 7 mm long and 3 mm thick (Tables 10, 10a). 
An isthmus is not present in this species and only 
small strips of each ventral wall are visible ventrally. 
The gland, whose surface is smooth and without 
conspicuous lobulation, is of the alveolar type. 
The follicles composing the gland are lined by simple cuboidal epi- 
thelium and vary in size up to 100^ m. The epithelial cells secrete the 
colloid which is subsequently stored in the follicular lacunae and con- 
tains the thyroid hormones, tri- and tetra-iodothyronin (Fig. 3-22). 
Production and release of the thyroid hormones 
are controlled by the thyrotropic pituitary hormone 
(TSH). Histometrically, small follicles indicate a 
high secretory activity, while large follicles a low 
activity (Neumann, 1963; Eickhoff, 1965; Warner, 
1971; Matthiesen and Messow, 1972; Messow, et 
ai, 1973). A change in cylindrical epithelial cells 
from large to small nuclei indicates reduced activity 
(Warner, 1971; Matthiesen and Messow, 1972; 
Messow, et ai, 1973). Based on follicle size and 
nuclear volume, both males and females showed 
maximum glandular activity in October before the 
onset of hibernation. The male thyroid activity was 
lowest during hibernation, while female activity 
was lowest in May following hibernation. 
The parathyroid is a paired gland consisting of 
two oval glandular bodies located dorsolaterally 
within the thyroid gland. 
The glandular structure is compact with interstitial capillaries and 
sparse connective tissue elements surrounding epithelial cells in cord 
or cluster patterns. Two cell types can be differentiated with hema- 
toxylin-eosin staining; the water-dear cells are regarded as the site of 
parathyroid hormone production; the chief cells are thought to be 
inactive, depot phases of the water-clear cell (Leonhardt, 1 97 1 ). 
In both males and females the peak number of 
cells and nuclear volume in the water-clear com- 
ponent occurred during hibernation, with the 
fewest in May after reanimation. 
69 
