574 



OF THE NECK. 



covers 

 triangle ; 



Dissection. 



External 

 iugular 



crosses side 

 of neck to 

 subclavian. 



Cervical 

 fascia. 



Part behind 

 sterno- 

 mastoid 

 muscle 



sends a 

 process 

 around 

 omo-hyoid. 



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 scattered, but they increase in strength as they 

 ascend. The oblique direction 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 transversely. 



The action will be found with the description of the remainder 

 of the muscle (p. 579). 



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

 and to be reflected forwards 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 of the external jugular vein, with the superficial descend- 

 ing branches of the cervical plexus, which are close beneath the 

 platysma, and which he should dissect out. 



The EXTERNAL JUGULAR VEIN (fig. 210, 8 p. 576) begins just 

 behind the angle of the jaw by the union of the posterior division 

 of the temporo-rnaxillary with the posterior articular vein (fig. 211, 

 p. 582). Descending beneath the platys.na to the lower part of 

 the neck, it there pierces the deep cervical fascia to open into the 

 subclavian vein. Its course down the neck will be marked by at 

 line from the angle of the jaw to the middle of the clavicle. Beyond 

 the sterno-mastoid muscle the vein is dilated, and the swollen part 

 (sinus) is limited by two pairs of valves, one being situate below 

 at the mouth of the vein, and the other near the muscle. Small 

 superficial branches join the vein, and an offset connects it with the 

 anterior jugular vein. Its size and the height at which it crosses 

 the sterno-mastoid muscle, are very uncertain. 



The DEEP CERVICAL FASCIA, like the aponeuroses in other 

 regions of the body, consists of a superficial layer which surrounds 

 the neck continuously, and of processes that are prolonged inwards 

 between the muscles. In some bodies this fascia is thin and indistinct. 



In its extent round the neck the membrane encases the sterno- 

 mastoid, and has a different disposition before and behind that 

 muscle. As now seen passing backwards from the muscle, the 

 fascia continues over the posterior triangular space, and encloses the 

 trapezius in its progress to the spines of the vertebrae. At the 

 lower part of the neck it is attached to the clavicle, and is 

 perforated by the external jugular vein and the cutaneous nerves. 



After the superficial layer has been removed near the clavicle, a 

 deep process may be observed surrounding the omo-hyoid muscle, 

 and passing downwards behind the clavicle, to be fixed at the back 

 of that bone, and the anterior end of the first rib. 



POSTERIOR TRIANGULAR SPACE. 



triangular 



This space (fig. 210), having the form and position before noted 

 theneck * s a ^ out e ig nt inches in length. It contains the cervical and brachial 



