128 



THE SKELETON. 

 Angle.' 



/Tnberosity. 



>; 



Articular part of tnbentsityS N^JC "\.. A'ccA 



five they are all united, and this portion of bone 

 consists of one piece (Fig. 82). The ensiform car- 

 tilage becomes joined to the gladiolus about forty. 

 The manubrium is occasionally, but not invariably, 

 joined to the gladiolus in advanced life by bone. 

 When this union takes place, however, it is gen- 

 erally only superficial, a portion of the centre of 

 the sutural cartilage remaining unossified. 



Articulations. With the clavicles and seven 

 costal cartilages on each side. 



Attachment of Muscles. To nine pairs and 

 one single muscle: the Pectoralis major, Sterno- 

 cleido-mastoid, Sterno-hyoid, Sterno-thyroid, Tri- 

 angularis sterni, aponeuroses of the Obliquus 

 externus, Obliquus internus, Transversalis, Rectus 

 muscles, and Diaphragm. 



The Ribs. 



The Ribs are elastic arches of bone, which form 

 the chief part of the thoracic walls. They are 

 twelve in number on each side ; but this number 

 may be increased by the development of a cervical 

 or lumbar rib, or may be diminished to eleven. 

 The first seven are connected behind with the spine 

 and in front with the sternum, through the inter- 

 vention of the costal cartilages ; they are called 

 true ribs. 1 The remaining five are false ribs; of 

 these, the first three have their cartilages attached 

 to the cartilage of the rib above : the last two are 

 free at their anterior extremities; they are termed 

 floating ribs. The ribs vary in their direction, 

 the upper ones being less oblique than the 

 lower. The extent of obliquity reaches its 

 maximum at the ninth rib, and gradually 

 decreases from that rib to the twelfth. The" 

 ribs are situated one below the other in such 

 a manner that spaces are left between them, 

 which are called intercostal spaces. The 



length of these spaces corresponds to the length of the ribs and their cartilages ; 

 their breadth is greater in front than behind, and between the upper than between 

 the lower ribs. The ribs increase in length from the first to the seventh, when 



1 Sometimes the eighth rib cartilage articulates with the sternum ; this condition occurs more 

 frequently on the right than on the left side. 



FIG. 85. A central rib of left side. 



