RESPIRATORY SYSTEM. OP 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 oesophagus from the thoracic inlet to the thyroid 

 gland. The two lobes are large at the root of the neck, where they are in apposition 



FiQ. 485. — Thymus of Young Calf. 



a, Thymus (cervical part) ; 6, trachea; c, isthmus of thyroid gland ; d, laryngeal prominence; i, apical lobe of right lung; 



«, heart (left ventricle) ; 3, pulmonary artery; 4, aorta; 5, 5', oesophagus; 6, m. longus oolH; 7, diaphragm. 



and cover the trachea, oesophagus, 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 tprojection, 

 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 



