l62 



HUMAN ANATOMY. 



rib between the head and the tubercle. Those for the last two ribs are small, that 

 for the twelfth springing from the accessory tubercle. The superioi' costo-transverse 

 ligaments ^ are thin bands, passing downward and a little inward from the under side 

 of the transverse processes to the crest on the upper edge of the neck of the rib 

 below. Those of the first and last two ribs are of litde account. This band becomes 

 tense when the rib is depressed and carried inward ; the inner fibres are tense when 

 the rib is raised. The outer fibres fuse with the front surface of the posterior inter- 

 costal aponeurosis. Weaker and inconstant bands of the same general direction are 

 described behind these. The fibres of the aponeurosis are particularly strong 

 between the last two ribs. A special band of the same series runs from the 

 transverse process of the first lumbar upward and outward to the last rib. The 

 movements of the ribs are described with those of the thorax (page 165). 



THE THORAX AS A WHOLE. 



The thorax is a cage with movable walls capable of expansion. In shape it is 

 an irregular truncated cone, much deeper behind than in front and broader from side 

 to side than from before backward. The thoracic vertebrae form the posterior 



Fig. 186. 



Tubercle -m'^ 



Lamina of VII thoracic 

 vertebra 



Middle costo-transverse 

 ligament 



Posterior costo-transverse 

 ligament 



Superior costo-transverse 

 ligament 



Ligamentum subflavum 



Intertransverse ligament 



VII thoracic rib 



VIII rib 



IX rib 



, Ligaments uniting ribs with spine, from behind. 



boundary ; the sternum, including the very beginning of the ensiform cartilage, the 

 anterior. The inlet, or upper boundary, is an imaginary plane slanting downward 

 and forward from the top of the first thoracic vertebra to that of the sternum, and 

 bounded laterally by the inner borders of the first rib. The inferior boundary, made 

 by the diaphragm, does not exist in the skeleton. Sufifice it to say that the dome- 

 like disposition of the diaphragm makes the abdomen much larger and the thorax 

 much smaller than one would expect from the skeleton alone. The thorax of the 

 living presents a fairly well-defined posterior surface, while the lateral ones pass in- 

 sensibly into the anterior ; the upper part is hidden by the shoulder-girdle and arm. 

 The line of the angles of the ribs marks the limits of the back and sides. The inside 

 of the thorax is heart-shaped in horizontal section. The spine projects into it behind, 

 and the ribs recede from this on either side. As the bodies of the vertebrae are 

 larger in the lower part, the projection into the thorax is greater ; but as the area of 

 the section is much larger, the effect is less striking. The distance from front to 



^ Lig. costotransversarium anterius. 



