THE THORAX Oil CHEST 



191 



The Ribs (Plate XXXVII).— We have already pointed out that there 

 are eighteen ribs on each side, distinguished numerically as the first, 

 second, third, and so on. The first eight are attached to the sternum and 

 designated true ribs. The remaining ten, having no such connection, are 

 called false ribs. Although they are thus distinguished, they all possess 

 certain common characteristics. They are long, flat, more or less curved 

 or arched outward from the chest, and are, besides, somewhat twisted on 

 themselves. They are all connected with the vertebrae above liy two free- 

 moving joints, and 

 below they are at- 

 tached to rods of car- 

 tilage {costal carti- 

 lages), through which 

 the first eight become 

 united by synovial 

 articulations to the 

 upper part of the 

 side of the sternum, 

 as already explained. 

 Each rib possesses a 

 head, a neck, and a 

 tubercle at the su- 

 perior extremity. The 

 head fits into a hollow 

 formed l)etween the 

 bodies of two verte- 

 brae, where it is united 

 by ligaments to form 

 a free -moving joint. 

 The tubercle forms 

 another synovial articulation with the transverse process of the vertebra 

 behind. The length of the ribs varies with the position they occupy. 

 From the first to the ninth they increase in length, and then progressively 

 they diminish to the last. Variation is also noticeable in the width, which 

 increases from the first to the sixth or seventh, and then diminishes to 

 the eighteenth. 



The outward curve they make increases from the first to the last, and 

 gives rotundity to the body in proportion as it is great or otherwise. 



Costal Cartilages. — These are cylindrical pieces of cartilage extend- 

 ing in a forward direction from the lower extremities of the ribs, which 

 they serve to elongate. The first eight are united with the sternum, and 



Fig. 294. — Pelvis (Superior Aspect) 



1 Antero-inferior Spine of Ilium. - Siipero-posterior Spine of Ilium. 



3 Obturator Foramen. ■■ Later.al Ischiatic Notch. ^ Tuberosity of Ischium. 

 8 Ischiatic Arch. " Symphysis Ischii. * Symphysis Pubis. 



