62 DISSECTION OF THE NECK. 



of the neck, near the position of the carotid vessels; and behind the muscle, 

 just above the clavicle, is another slight hollow which points to the situa- 

 tion of the subclnvian artery. 



Along the middle line of the neck the following parts can be recognized 

 through the skin : About two inches and a half from the base of the jaw 

 is the eminence of the os hyoides, with its cornu extending laterally on 

 each side. Below this may be felt the wide prominence of the thyroid 

 cartilage, called pomum Adami, which is most marked in man : and be- 

 tween the cartilage and the hyoid bone is a slight interval, corresponding 

 with the thyro-hyoid membrane. 



Inferior to the thyroid, is the narrow prominent ring of the cricoid car- 

 tilage ; and between the two the finger may distinguish another interval, 

 which is opposite the crico-thyroid membrane. In some bodies, especially 

 in women, the swelling of the thyroid gland may be felt by the side of the 

 trachea. 



From the cricoid cartilage to the sternum, and between the sterno-mas- 

 toid muscles, is a depression, whose depth is much increased in emaciated 

 persons, in which the tube of the trachea can be recognized. 



Direction. As the time for turning the body will not allow the examina- 

 tion of the whole side of the neck, the student should lay bare in this stage 

 only the parts behind the sterno-mastoid muscle. 



Dissection. To raise the skin from the posterior triangle of the neck, 

 make an incision along the sterno-mastoid muscle from the one end to the 

 other, and afterwards along the clavicle as far as the acromion. The tri- 

 angular flap of skin is to be reflected from before back towards the trapezius 

 muscle. The superficial fascia which will then be brought into view, con- 

 tains the platysma ; and to see that muscle, it will be necessary to take the 

 subcutaneous fat from the surface of the fibres. 



The PLATISMA MYOIDES is a thin subcutaneous muscular layer, which 

 is now seen only in its lower half. The muscle is placed across the side 

 of the neck, and extends from the top of the shoulder to the face. Its 

 fleshy fibres take origin by fibrous bands from the clavicle and the acro- 

 mion, and below those bones from the superficial fatty layer covering the 

 pectoral and deltoid muscles ; ascending through the neck, the fibres are 

 inserted into the jaw. 



The lower part of the muscle is more closely united to the skin than the 

 upper, and covers the external jugular vein as well as the lower part of 

 the posterior triangle. At first the fibres of the muscle are thin and scat- 

 tered, but they increase in strength as they ascend. The oblique direc- 

 tion of the fibres should be noted, because in venesection in the external 

 jugular vein the incision is to be so made as to divide them across. 



The use will be found with the description of the remainder of the 

 muscle. 



Dissection. The platysma is now to be cut across near the clavicle, 

 and to be reflected upwards as far as the incision over the sterno-mastoid 

 muscle, but it is to be left attached at that spot. In raising the muscle 

 the student must be careful of the deep fascia of the neck ; and he should 

 dissect out the external jugular vein, and the superficial descending 

 branches of the cervical plexus, which are close beneath the platysma. 



The external jugular vein (fig. 14, 8 ) commences in the parotid gland 

 (p. 42), and is directed backwards beneath the platysma to the lower part 

 of the neck, where it pierces the deep cervical fascia to open into the sub- 

 clavian vein. Its course down the neck will be marked by a line from 



