GUIDE TO THE HEAD AND NECK i^B? 



examined. The crico-thyroid muscle is to be studied in so far as it can 

 be seen without interfering with the thyroid cartilage, and its nerve- 

 supply, namely, the external laryngeal nerve, is to be carefully noted. The 

 part of the crico-thyroid membrane between the two crico-thyroid muscles 

 has been already studied in connection with the operation of laryngotomy. 

 The larynx being now placed upon its side, the greater part of the ala of the 

 thyroid cartilage is to be removed by making (i) a vertical cut through it 

 not far from the median line, and stopping short of the lower border, and 

 (2) a horizontal cut extending backwards from the lower end of the vertical 

 cut. A complete view will now be obtained of the crico-thjnroid muscle, 

 which should be removed. Thereafter the following muscles fall to be dis- 

 sected, namely, the lateral crico-arjrtenoid, the thyro-arytenoid, and the 

 thyro-epiglottideus. An effort should be made to show the two portions 

 of the thyro-arytenoid muscle, namely, internal and external ; and the 

 close relation of the internal portion to the true vocal cord is to be noted. 

 The lateral crico-arytenoid, and the whole of the thyro-arytenoid, muscles are 

 to be very carefully removed. This will expose the lateral portion of the 

 crico-thyroid membrane, the inferior thjrro-arytenoid ligament or true vocal 

 cord, and the wall of the ventricle of the larynx. Above the wall of the ven- 

 tricle the fibres of the superior thyro-arytenoid ligament, which enter into the 

 false vocal cord, will be found. The mucous membrane above the true vocal 

 cord may now be removed on the side which is being dissected, when the true 

 and false cords of the opposite side may be examined, with the ventricle of the 

 larynx lying between them. The saccule, which is connected with the anterior 

 part of the ventricle, is to be explored with a probe. During the course of 

 the foregoing dissections it is presumed that the dissectors, as recommended, 

 have been keeping in view the nerves and arteries of the larynx. 



The ligaments of the larynx will have been displayed in the course of the 

 dissection, these ligaments being the thyro-hyoid membrane, the crico- 

 thyroid membrane, the superior thyro-arytenoid ligament, and the inferior 

 thyro-arytenoid ligament. Two joints require close attention, namely, the 

 crico-thyroid and the crico-arytenoid joints, and the movements allowed at 

 these articulations are to be carefully studied. The varying conditions 

 assumed by the rima glottidis will be found described in the text. The 

 actions of the laryngeal muscles are to be studied with the closest attention, 

 and the function of the epiglottis is to be considered. 



Prevertebral Muscles. — The scedene muscles — anticus, medius, and posticus, 

 if not previously dissected, should now be examined, followed by the rectus 

 capitis anticus major, rectus capitis anticus minor, rectus capitis lateralis, and 

 longus colli. 



The vertebral artery, as it traverses the costo-transverse foramina of the 

 upper six cervical vertebrae, is to be dissected, and the plexiform arrangement 

 of veins around it is to be noted. The vertebral plexus of the sympathetic 

 is also to be borne in mind. 



The Ear. — The meatus auditorius extemus is to be laid open with the chisel 

 and bone-pliers, and the membrana tympani is to be carefully examined from 

 the outside. The upper part of the membrane, called the membrana flaccida. 

 or Shrapnell's membrane, which is attached to the notch of Rivini, is to receive 

 special attention. The handle of the malleus will be observed extending 

 between the mucous and fibrous layers of the membrane to a point a little 

 below its centre, where the membrane is drawn inwards so as to give rise ex- 

 ternally to a slight depression, known as the umbo. To expose the cavity of 

 the tympanum, an opening is to be made through the thin lamina of bone, 

 called the tegmen tympani, which is situated on the superior surface of the 

 petrous portion of the temporal bone. If this opening is made external to the 

 eminentia arcuata, it will expose the mastoid antrum. The opening is then 

 to be enlarged with the bone-pliers, and the canal containing the tensor 

 tympani muscle is to be laid open. The meatus auditorius intemus may 

 also be laid open. The tympanic cavity, with its intricate contents, the 

 tensor t>Tnpani muscle, and the osseous part of the Eustachian tube, are now 

 available for examination. The contents of the meatus auditorius intemus 

 are to be held over in the meantime. The ossicles of the tympanum, namely. 



