DEEP BRANCHES OF THE CEKVICAL PLEXUS. H99 



?he deep set of branches remains to be examined : they are and deep, 

 nuscular and communicating, and may be arranged in an internal w 

 nd an external series. 



DEEP SET OF BRANCHES OF THE CERVICAL PLEXUS. 1. INTERNAL Phrenic 



ERIES. The phrenic or muscular nerve of the diaphragm is ne 

 erived from the fourth, or third and fourth nerves of the plexus ; 

 nd it may be joined by a fasciculus from the fifth cervical nerve. 

 )escending obliquely on the surface of the anterior scalenus 

 fig. 213) from the outer to the inner edge, it enters the chest 

 n front of the internal mammary artery, but behind the subclaviau 

 r ein, and traverses that cavity to reach the diaphragm. At the 

 >wer part of the neck the phrenic nerve is joined by a filament of 

 he sympathetic, and sometimes by an offset of the nerve to the 

 Libclavius muscle. 



On the left side the nerve crosses over the first part of the 

 ibclavian artery. 



The branches to the ansa cervicis are two in number: one arises Nerves to 

 rom the second, and the other from the third cervical nerve. They ^^ 

 re spoken of as the communicant es cervicis nerves and are directed 

 ii wards over or under the internal jugular vein to join in a loop with 

 lie descendens cervicis branch (p. 602) of the hypoglossal nerve in 

 out of the common carotid artery. The loop of the communication 

 f the nerves over the carotid artery is called the ansa cervicis. 



Muscular branches are furnished to the rectus anticus major and Branches to 

 mgus colli muscles from the trunks of the nerves close to the J2Jei? bral 

 iter vertebral foramina. 



Some muscular and connecting branches from the loop between the Branches of 



.,, , , first nerve, 



rst two nerves will be afterwards seen. 



2. EXTERNAL SERIES. Muscular branches are supplied from the 

 econd nerve to the sterno-mastoid ; from the third and fourth 

 ves to the levator auguli scapulae and middle scalenus ; and 

 rum the loop between the same nerves to the trapezius. 



< ' 'nitnectwg branches with the spinal accessory nerve exist in three Branches 

 >laces. First, in the sterno-mastoid muscle ; next, in the posterior ip'inai 8 

 riangular space ; and lastly, beneath the trapezius. The union accessory, 

 with the branches distributed to the trapezius has the appearance of 

 plexus. 



The COMMON CAROTID ARTERY is the chief vessel for the supply Common 

 f blood to the neck and head (fig. 213, 6 ). The origin of the artery: 

 essel differs on the two sides, being at the lower part of the neck 

 311 the right side, and in the thorax on the left side. 



The cause and relations of the left artery in the neck are the same 

 s those on the right side, and the description serves for both. (The 

 art of the left common carotid artery in the thorax has been 

 described on page 468.) 



The right vessel commences opposite the sterno-clavicular articu- origin 

 lation at the bifurcation of the innominate artery on the right side, 

 and prolonged up from the thorax on the left, and ends at, or a 

 little above, the upper border of the thyroid cartilage, on a level 

 with the fourth cervical vertebra, by dividing into external and 



