RESPIRATORY SYSTEM OF THE PIG—THE NASAL CAVITY 545 
with the chest-wall and apical lobe of the left lung as far back as the third rib. 
Its right face is largely molded on the great vessels in front of the heart. The 
cervical part forms the bulk of the gland; it consists of right and left lobes which 
extend along the trachea and cesophagus from the thoracic inlet to the thyroid 
gland. The two lobes are large at the root of the neck, where they are in apposition 
Fic. 485.—Tuymus oF Youne Car. 
a, Thymus (cervical part); 5, trachea; c, isthmus of thyroid gland; d, laryngeal prominence; 1, apical lope of right lung; 
2, heart (left ventricle); 3, pulmonary artery; 4, aorta; 5, 5’, esophagus; 6, m. longus colli; 7, diaphragm. 
and cover the trachea, cesophagus, carotid artery, and vago-sympathetic trunk. 
Further forward they gradually diminish in size and diverge to the sides of the 
trachea. They are related superficially to the sterno-cephalicus, sterno-thyro- 
hyoideus, and external jugular vein. It undergoes atrophy slowly and remnants 
of the thoracic part often remain even in advanced age. 
RESPIRATORY SYSTEM OF THE PIG 
THE NASAL CAVITY 
The nostrils are small, and are situated on the flat anterior surface of the 
rostrum or snout (Rostrum suis). The latter is a short cylindrical projection, 
with which the upper lip is fused, and is circumscribed by a prominent circular 
margin. The skin on the snout is thin and highly sensitive; it presents small 
pores, and scattered over it are fine short hairs. In the snout between the nostrils 
is the os rostri, which is to be regarded as a special development of the extremity of 
the septum nasi in adaptation to the habit of burrowing or rooting. A plate of 
cartilage, representing the lamina of the alar cartilage of the horse, curves ventro- 
laterally from the dorsal part of the os rostri, and a pointed bar of cartilage curves 
upward from the lower part of the bone in the lateral wing of the nostril. The 
notch between the nasal bone and the premaxilla is closed in by parietal cartilages 
which resemble those of the ox. 
The nasal cavity (Fig. 180) is long and narrow. It is divided behind by the 
lamina transversalis into an upper olfactory part, which leads to the ethmoidal 
meatuses, and a lower respiratory part, which is a direct continuation of the ventral 
meatus. The posterior part of the septum is membranous. The turbinate bones 
resemble in general those of the ox. The dorsal meatus is exceedingly small. The 
middle meatus is a deep fissure between the two turbinates: it divides posteriorly 
35 
