SECTION Til 



THE THOKAX 



INCLUDING THE ORGANS OF VOICE, 

 RESPIRATION, AND CIRCULATION 



By ARTHUR HENSMAX, F.R.C.S. 

 Revised for Second Edition by ARTHUR ROBINSON, M.Tt., M.R.C.S. 



LECTURER ON ANATOMY IN THE MIDDLESEX HOSPITAL MEDICAL SCHOOL ; EXAMINER IN ANATOMY FOR THE 



CONJOINT BOARD OF ENGLAND 



THE THORAX 



THE thorax, or trunk of the body — l3'ing between the neck and the al)domen — 

 is formed partly of bones and partly of soft connecting tissues. In the living 

 l)ody it is constantly varying in relation to the respiratory process. The cavity 

 is bounded in front by the sternum and upper six costal cartilages and internal 

 intercostal muscles; behind by the thoracic veitebrse and posterior ends of the 

 ribs; and laterally by the ribs with the internal and external intercostal muscles. 



Its form is conical, flattened in the adult from before backwards, so that its 

 transverse is its greater diameter. In the human foetus, as in the lower animals, 

 it is flattened laterally, its antero-posterior diameter being the greater. 



It is narrow above, where the ribs are short, and broad below. Owing to the 

 backward set of the hinder extremities of the ril)s, the bodies of the vertebne pro- 

 ject forwards into the cavity, which thus, on a transverse section, appears more or 

 less cordiforni. 



The superior aperture is Ixjundcd, in front by the upper margin of the ster- 

 num; behind by the body of the first thoracic vertebra; on each side l)y the first 

 rib. It measures in a well-formed adult al)out two and a quarter inches from l)efore 

 l)ackwards, and four and a quarter inches from side to side. The ribs slope down- 

 Avards towards the sternum, the upper margin of Avhich corresponds to the inter- 

 vcrtel^ral substance l^etween the second and tliird thoracic vertel)ra'. It transmits 

 the following structures: — (1) The sterno-hyoid and sterno-thyroid nuiscles. and 

 more deeply a thin layer of the deep cervical fascia whicli blends below with the 

 sheath of the great vessels and the pericardium; (2) the tliynnis gland in the infant, 

 or its shrunken remains in the adult; (3) an occasional middle thyroid artery, the 

 trachea, the oesophagus, the thoracic duct, the longus colli muscles, and a thin layer 

 of fascia overlying them. Laterally: the innominate artery (on the right side), the 

 common carotid and subclavian (on the left), with the internal mannnary and 

 superior intercostal arteries; the innominate and inferior thyroid veins; the phrenic, 

 pneumogastric, and sympathetic nerves. Avith the left recurrent laryngeal, some 

 cardiac l>ranches, and the anterior ])ranches of the first thoracic nerve. On each 



898 



