POSTERIOR TRIANGULAR SPACE. 63 



the angle of the jaw to the middle of the clavicle. Beyond the sterno- 

 mastoid muscle the vien 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 consists, like the aponeuroses in other regions 

 of the body, 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 incases the sterno-mas- 

 toideus, and presents 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 incloses 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 to surround the small omo-hyoid muscle, and to 

 extend under the clavicle, where it is fixed to the back of that bone, and 

 the inner end of the first rib. 



POSTERIOR TRIANGULAR SPACE. 



This space (fig. 14), having the form and position before noted, is about 

 eight inches in length. It contains the cervical and brachial plexuses, with 

 the portion of the subclavian artery on which a ligature is usually placed, 

 and some offsets of the vessel and the nerves. 



Dissection. By the removal of the cervical fascia and the fat between 

 the sterno-mastoid and trapezius muscles, the posterior triangle of the 

 neck will be displayed. In the execution of this task, the student may 

 obtain some assistance by attending to the following remarks : 



Crossing the space obliquely about an inch above the clavicle, and 

 dividing it into two, is the small omo-hyoid muscle (fig. 14, s ). Close to 

 or under the upper border of the muscle lie the small nerve and vessels to 

 it : the nerve being traceable to the descendens noni, and the artery to the 

 supra-scapular. 



Above the omo-hyoid muscle will be found the ramifications of the 

 branches of the cervical plexus, together with the spinal accessory nerve ; 

 the latter will be recognized by its piercing sterno-mastoid muscle. The 

 greater number of the branches of the cervical plexus descend. in the space 

 to the shoulder ; but the small occipital and great auricular nerves ascend 

 to the head, and the superficial cervical branch is directed forwards over 

 the sterno-mastoid muscle. 



Below the omo-hyoideus are the subclavian artery and the brachial 

 plexus, which have a deep position. In this part also the following ves- 

 sels and nerve are to be sought, viz., the supra-scapular vessels behind the 

 clavicle ; the transverse cervical vessels which are higher in the neck, but 

 take an outward direction beneath the omo-hyoid muscle ; and, lastly, the 

 small branch of nerve to the subclavius muscle, which lies about the mid- 

 dle of the space between the clavicle and omo-hyoideus. 



Underneath the trapezius, where it is attached to the clavicle, the 



