228 THE SKELETON. 



of the Digastric, Stylo-hyoid, Mylo-hyoid, Genio-hyoid, Genio-hyo-glossus, Chon- 

 dro-glossus, Hyo-glossus, Middle constrictor of the pharynx, and occasionally a few 

 fibres of the Lingualis. It also gives attachment to the thyro-hyoidean membrane 

 and the stylo-hyoid, thyro-hyoid, and hyo-epiglottic ligaments. 



Surface Form. The hyoid bone can be felt in the receding angle below the chin, and the 

 finger can be carried along the whole length of the bone to the greater cornu, which is situated 

 just below the angle of the jaw. This process of bone is best perceived by making pressure on 

 one cornu, and so pushing the bone over to the opposite side, when the cornu of this side will 

 be distinctly felt immediately beneath the skin. This process of bone is an important landmark 

 in ligature of the lingual artery. 



Surgical Anatomy. The hyoid bone is occasionally fractured, generally from direct vio- 

 lence, as in the act of garrotting or throttling. The great cornu is the part of the bone most fre- 

 quently broken, but sometimes the fracture takes place through the body of the bone. In con- 

 sequence of the muscles of the tongue having important connections with this bone, there is 

 great pain upon any attempt being made to move the tongue, as in speaking or swallowing. 



THE THORAX. 



The Thorax, or Chest, is an osseo-cartilaginous cage containing and protecting 

 the principal organs of respiration and circulation. It is conical in shape, being 

 narrow above and broad below, flattened from before backward, and longer behind 

 than in front. It is somewhat cordiform on transverse section. 



Boundaries. The posterior surface is formed by the twelve dorsal vertebrae 

 and the posterior part of the ribs. It is convex from above downward, and pre- 

 sents on each side of the middle line a deep groove inconsequence of the direction 

 backward and outward which the ribs take from their vertebral extremities to 

 their angles. The anterior surface is flattened or slightly convex, and inclined 

 forward from above downward. It is formed by the sternum and costal cartilages. 

 The lateral surfaces are convex ; they are formed by the ribs, separated from each 

 other by spaces, the intercostal spaces. These are eleven in number, and are 

 occupied by the intercostal muscles. 



The upper opening of the thorax is reniform in shape, being broader from side 

 to side than from before backward. It is formed by the first dorsal vertebra 

 behind, the upper margin of the sternum in front, and the first rib on each side. 

 It slopes downward and forward, so that the anterior part of the ring is on a 

 lower level than the posterior. The antero-posterior diameter is about two inches. 

 The lower opening is formed by the twelfth dorsal vertebra behind, by the twelfth 

 rib at the sides, and in front by the cartilages of the eleventh, tenth, ninth, eighth, 

 and seventh ribs, which ascend on either side and form an angle, the subcostal 

 angle, from the centre of which the ensiform cartilage projects. It is wider trans- 

 versely than from before backward. It slopes obliquely downward and backward, 

 so that the cavity of the thorax is much deeper behind than in front. The Dia- 

 phragm closes in the opening forming the floor of the thorax. 



In the female the thorax differs as follows from the male : 1. Its general 

 capacity is less. 2. The sternum is shorter. 3. The upper margin of the sternum 

 is on a level with the lower part of the body of the third dorsal vertebra, whereas 

 in the male it is on a level with the lower part of the body of the second dorsal 

 vertebra. 4. The upper ribs are more movable, and so allow a greater enlargement 

 of the upper part of the thorax than in the male. 



The Sternum. 



The Sternum (orsovov, the chest) (Figs. 179, 180) is a flat, narrow bone, sit- 

 uated in the median line of the front of the chest, and consisting, in the adult, of 

 three portions. It has been likened to an ancient sword; the upper piece, repre- 

 senting the handle, is termed the manubrium ; the middle and largest piece, which 

 represents the chief part of the blade, is termed the gladiolus ; and the inferior 

 piece, which is likened to the point of the sword, is termed the ensiform or xiphoid 

 appendix. In its natural position its inclination is oblique from above downward 

 and forward. It is flattened in front, concave behind, broad above becoming 



