71 



is formed by the nasal, superior maxillary, lacrymal, ethmoid, 

 inferior turbinate, palate, and internal pterygoid plate of the 

 sphenoid. The superior and inferior turbinate processes of 

 the ethmoid and the inferior spongy bone overhang the three 

 meatuses. The superior meatus is very short, and placed be- 

 tween the superior and inferior turbinate processes; into it 

 open in front the posterior ethmoidal cells, and behind the 

 sphenopalatine foramen. The middle meatus is above the 

 inferior spongy bone, and communicates with the anterior 

 and middle ethmoidal cells, with the maxillary sinus or antrum, 

 and in front by the infundibulum with the frontal sinus. The 

 inferior meatus, longer than the others, lies between the inferior 

 spongy bone and the floor of the cavity; in front is the orifice 

 of the nasal duct. 



The air sinuses communicate with the basal cavities by 

 narrow orifices; with the exception of the maxillary sinus 

 (antrum) they are not present at birth. In old age they increase 

 in size by absorption of neighboring cancellated tissue. The 

 antrum begins to be formed about the fourth month. The 

 frontal, ethmoidal, and sphenoidal excavate their respective 

 bones in childhood, and at puberty undergo a great enlarge- 

 ment. Their purpose may be for resonance. They have 

 been sufficiently described with the different bones. 



THE THORAX 



The Thorax as a Whole 



The bony thorax is conical, and flattened from before back- 

 ward. The short anteroposterior diameter is characteristic 

 of man, but in the lower mammals and human fetus it is longer 

 than the transverse diameter. The posterior wall is convex 

 forward, and a broad furrow on either side, the sulcus pulmo- 

 nalis, is formed by the ribs as they project backward, so that 

 the weight of the body is more equally distributed around the 

 column. The anterior wall is convex and at an angle of 20 

 to 25 degrees with the posterior. A horizontal anteroposterior 

 diameter from the base of the ensiform is 8 inches (20 cm.); 

 the transverse at the eighth or ninth rib is 11 inches (28 cm.); 

 the vertical anteriorly is 6 inches (15,5 cm.), and posteriorly 



