122 



RESPIRATION. 



ribs posteriorly, by the upper ten ribs laterally, and by the sternum and costal cartilages 

 anteriorly. The direction of the ribs, their mode of connection wiiih the sternum by the 

 costal cartilages, and their articulation with the vertebral column, are such that, by their 

 movements, the antero-posterior and transverse diameters of the chest may be consider- 

 ably modified. 



Inspiration. 



The ribs are somewhat twisted upon themselves and have a general direction forward 

 and downward. The first rib is nearly horizontal, but the obliquity of the ribs progressively 

 increases from the upper to the lower parts of the chest. They are articulated with the 

 bodies of the vertebrae, so as to allow of considerable motion. The upper seven ribs are 

 attached by the costal cartilages to the sternum, these cartilages Tunning upward and 



FIG. 40. Thorax, anterior mew. (Sappey.) 



1, 2, 3, sternum ; a. circumference of the upper portion of 

 the thorax: 5, circumference of the base of the 

 thorax; 6, first rib; 7, second rib; 8, 8, last five ster- 

 nal ribs ; 9, upper three false ribs ; 10, last two, or 

 floating ribs ; 11, costal cartilages. 



FIG. 41 . Thorax, posterior view. (Sappey . ) 

 1, 1, spinous processes of the dorsal vertebrse; 2, '2, 

 laminae of the vertebrae ; 8, 3, transverse processes ; 

 4, 4, dorsal portions of the ribs ; 5, 5, angles of the 

 ribs. 



inward. The cartilages of the eighth, ninth, and tenth ribs are joined to the cartilage 

 of the seventh. The eleventh and twelfth are floating ribs and are attached only to the 

 vertebrse. 



It may be stated, in general terms, that inspiration is effected by descent of the dia- 

 phragm and elevation of the ribs ; and expiration, by elevation of the diaphragm and 

 descent of the ribs. 



Arising severally from the lower border of each rib and attached to the upper border 

 of the rib below, are the eleven external intercostal muscles, the fibres of which have 

 an oblique direction from above downward and forward. Attached to the inner bor- 

 ders of the ribs are the internal intercostals, which have a direction from above downward 

 and backward, nearly at right angles to the fibres of the external intercostals. There are 

 also a number of muscles attached to the thorax and spine, thorax and head, upper part 

 of humerus, etc., which are capable of elevating either the entire chest or the ribs. 

 These must act as muscles of inspiration, when the attachments to the thorax become 

 the movable points. Some of them are called into action during ordinary respiration ; 

 others act as auxiliaries when respiration is a little exaggerated, as after exercise, and are 



