120 DISSECTION OF THE NECK. 



COMMON CAROTIDS. On opposite sides these vessels have differences 

 like those between the right and left subclavian arteries; for the left ves- 

 sel arises from the arch of the aorta, and is therefore deep in the chest, 

 and longer than the right. The description of the artery between its 

 origin and the top of the sternum will be included in the dissection of the 

 thorax. 



Beyond the sterno-clavicular articulation the vessels, on both sides, so 

 nearly resemble one another that the same description may serve for the 

 two (p. 81). On the left side, however, the jugular vein and the pneumo- 

 gastric nerve are much nearer to the carotid than on the right side, and 

 are placed over the artery in the lower third of the neck. 1 



PARTS IN THE UPPEK APERTURE OF THE THORAX. The relative po- 

 sition of the several parts entering or leaving the thorax by the upper 

 opening may be now observed. 



In the middle line lie the remains of the thymus gland, and the trachea 

 and oesophagus. In front of the trachea are the lower ends of the sterno- 

 hyoid and sterno-thyroid muscles with layers of the cervical fascia, and the 

 inferior thyroid veins ; and behind the gullet and windpipe is the longus 

 colli muscle. Between the two tubes is the recurrent nerve on the left 

 side. 



On each side the bag of the pleura and the apex of the lung project into 

 the neck; and in the interval between the pleura and the trachea and 

 O3sophagus, are placed the vessels and nerves passing between the thorax 

 and the neck. Most anteriorly on both sides lie the innominate vein, the 

 phrenic nerve, and the internal mammary artery ; but the vessels and 

 nerves next met with are different on the two sides. On the right side 

 come the innominate artery, with the vagus, the cardiac nerves, and the 

 right lymphatic duct ; but on the left side are the left vagus, the left com- 

 mon carotid artery, the thoracic duct, and the left subclavian artery with 

 the cardiac nerves. Lastly, altogether behind on each side are part of the 

 first intercostal nerve, the cord of the sympathetic, and the superior inter- 

 costal artery. 



The THYROID BODY is a soft reddish mass, which is situate opposite the 

 upper part of the trachea. It consists of two lobes, one on each side, 

 which are united by a narrow piece across the front of the windpipe. The 

 connecting piece, about half an inch in depth, is named the isthmus, and 

 is placed opposite the second and third rings of the air tube. 



Each lobe is somewhat conical in shape, with the smaller end upwards, 

 and is about two inches in length. It is interposed between the Avindpipe 

 and the sheath of the common carotid artery, and is covered by the sterno- 

 thyroid, sterno-hyoid, and omo-hyoid muscles. The extent of the lobe 

 varies ; but usually it reaches as high as the middle of the thyroid cartilage, 

 and as low as the sixtli ring of the trachea. 



From the upper part of the thyroid body, and most commonly from the 

 left lobe, a conical piece pyramid, ascends towards the hyoid bone, to 

 which it is connected by a fibrous band. Sometimes this part is attached 

 to the os hyoides by a slip of muscle, the levator glandulce. thyroidece of 

 Socmmering. 



This body is of a brownish red or purple hue, is granular in texture, 

 and weighs from one to two ounces. Its size is larger in the woman than 



1 Occasionally these differences will be reversed the vein and nerve being over 

 the artery on the right side, and away from it on the left. 



