THE PLEURAE 1183 



fascia, which, attached above to the lower border of the hyoid bone, descends beneath the muscles 

 to the thyroid body, where it divides into two layers and encloses the isthmus. 



Below the isthmus the trachea lies much more deeply, and is covered by the Sternohyoid 

 and the Sternothyroid muscles and a quantity of loose areolar tissue in which is a plexus of veins, 

 some of them of large size; they converge to two trunks, the inferior thyroid veins, which descend 

 on either side of the median line on the front of the trachea and open into the innominate vein. 

 In the infant the thymus gland ascends a variable distance along the front of the trachea, and 

 opposite the episternal notch the windpipe is crossed by the left innominate vein. Occasionallv, 

 also, in young subjects, the innominate artery crosses the tube obliquely above the level of the 

 sternum. The thyroidea ima artery, when that vessel exists, passes from below upward along 

 the front of the trachea. 



From these observations it must be evident that the trachea can be more readily opened above 

 than below the isthmus of the thyroid body. 



Tracheotomy above the isthmus is performed thus: The patient should, if possible, be laid 

 on his back on a table in a good light. A pillow is to be placed under the shoulders and the 

 head thrown back and steadied by an assistant. The surgeon, standing on the right side of his 

 patient, makes an incision from an inch and a half to two inches in length in the median line of 

 the neck from the top of the cricoid cartilage. The incision must be made exactly in the middle 

 line, so as to avoid the anterior jugular veins, and after the superficial structures have been 

 divided the interval between the Sternohyoid muscles must be found, the raphe divided, and 

 the muscles drawn apart. The lower border of the cricoid cartilage must now be felt for, and 

 the upper part of the trachea exposed from this point downward in the middle line. Bose has 

 recommended that the layer of fascia in front of the trachea should be divided transversely at 

 the level of the lower border of the cricoid cartilage, and, having been seized with a pair of for- 

 ceps, pressed downward with the handle of the scalpel. By this means the isthmus of the thyroid 

 gland is depressed, and is saved from all danger of being wounded, and the trachea is cleanly 

 exposed. The trachea is now transfixed with a sharp hook and drawn forward in order to 

 steady it, and is then opened by inserting the knife into it and dividing the two or three upper 

 rings from below upward. If the trachea is to be opened below the isthmus, the incision to 

 expose it must be made from a little below the cricoid cartilage to the top of the sternum. 



In the child the trachea is smaller, more deeply placed, and more movable than in the adult. 

 In fat or short-necked people, or in those in whom the muscles of the neck are prominently 

 developed, the trachea is more deeply placed than in others. 



A portion of the larynx or the whole of it has been removed for malignant disease, laryngec- 

 tomy. Some surgeons do preliminary tracheotomy, insert a Trendelenburg cannula to prevent 

 the flow of blood downward into the lungs, and then remove the larynx. Other surgeons do 

 not employ preliminary tracheotomy. Perier's method of laryngectomy is as follows: Make 

 a vertical incision in the median line from the level of the hyoid bone to below the level of the 

 cricoid cartilage. Make a transverse incision at each end cf the vertical incision. This* makes 

 an I-shaped wound. Separate the soft parts from the larynx and upper part of the trachea, and 

 separate these two structures from the oesophagus. After arresting bleeding, divide the trachea 

 below the cricoid cartilage, introduce a special cannula, complete the removal of the larynx, 

 suture the opening of the trachea to the lower angle of the wound, and close the rest of the wound 

 after securing drainage. In malignant disease of the larynx the associated lymph nodes must 

 be removed. Partial laryngectomy, according to Sir F. Semon, is the removal of not less than 

 one wing of the thyroid cartilage. Removal of a lesser piece of the thyroid or of a bit of the 

 arytenoid or cricoid he considers with the operation of thyrotomy. 



THE PLEUR-ffi (Figs. 879, 909). 



Each lung is invested by an exceedingly delicate serous membrane, the pleura, 

 which encloses the organ as far as its root, and is then reflected on to the peri- 

 cardium, thoracic wall, and Diaphragm. The portion of the serous membrane 

 investing the surface of the lung and dipping into the fissures between its lobes 

 is called the visceral layer of the pleura (pleura pulmonalis) (Fig. 897), while that 

 which lines the inner surface of the thorax is called the parietal layer of the pleura 

 (pleura parietalis) (Fig. S97). The space between these two layers is called the 

 cavity of the pleura (cavum pleurae], and contains a very little clear fluid. It must 

 be borne in mind that in the healthy condition the two layers are in contact, and 

 there is no real cavity. When the lung becomes collapsed a separation of it 

 from the wall takes place and a cavity results. Each pleura is therefore a shut 



