Adis ie alee 
THORACIC NERVES. 593 
SUBSCAPULAR NERVES. 
There are three subscapular nerves (nn. subscapulares) (Figs. 429 and 451). 
The first or short subscapular nerve is generally double, and there may be 
three trunks present. It arises from the posterior cord of the plexus behind the 
circumflex nerve, and from the fifth and sixth cervical nerves. It passes downwards 
behind the axillary artery and enters the subscapularis muscle. 
’ The second or lower subscapular nerve also arises behind the circumflex 
from the posterior cord of the plexus, and from the fifth and sixth cervical nerves. 
Its origin is below and external to that of the first nerve. It courses outwards and 
downwards behind the axillary artery, and below the circumflex and musculo- 
spiral nerves to the teres major muscle. It supplies branches to the outer part of 
the subscapularis muscle and ends in the teres major. 
The third or long subscapular nerve (n. thoraco-dorsalis) arises from the back 
of the posterior cord of the plexus, behind the musculo-spiral nerve, and from the 
sixth, seventh, and eighth cervical nerves, or from the seventh and eighth nerves only. 
It is directed downwards and outwards between the two previous nerves, behind the 
axillary artery and over the posterior wall of the axilla, in company with the sub- 
scapular artery, to the latissimus dorsi muscle, which it supplies on its anterior 
(inner) surface. 
THORACIC NERVES. 
The thoracic nerves are twelve in number, each nerve emerging below the 
corresponding vertebra and rib. Eleven of the series are intercostal, the twelfth 
lying below the last rib. The first, second, third, and twelfth nerves present 
peculiarities in their course and distribution. The other thoracic nerves, as already 
stated, are simple, and may be regarded as types both in course and distribution. 
The first thoracic nerve is the largest of the series. It emerges from the 
spinal canal below the neck of the first rib, and divides in the first intercostal 
space into two very unequal, upper and lower, parts. The wpper larger part ascends 
obliquely over the neck of the first rib, lying external to the superior intercostal 
artery, and enters the neck behind the subclavian artery and the pleura. It pro- 
ceeds outwards upon the scalenus medius muscle and enters into the formation of 
the brachial plexus, as already described. 
The lower, intercostal part of the nerve is much smaller in size. It courses 
forwards in the first intercostal space and supplies the intercostal muscles. It 
usually gives off no anterior branch to the skin of the chest and no lateral 
cutaneous branch. 
In some cases a lateral cutaneous branch emerges from the side of the first intercostal space. 
This may be derived from the first nerve, or it may be the intercosto-humeral nerve, derived 
from the second thoracic nerve. In many cases an anterior cutaneous branch perforates the first 
intercostal space and supplies the skin on the front of the chest. This branch, similarly, is some- 
times traceable to the second thoracic nerve. 
Communications. — Besides its junction with the eighth cervical to form the 
brachial plexus, the first thoracic nerve effects the following communications :—(a) The 
last cervical or first thoracic ganglion of the sympathetic sends a gray ramus communi- 
cans to join the nerve on its appearance in the thorax. (6) The second thoracic nerve in 
a majority of cases communicates with the first. This communication varies considerably 
in size and distribution. It may reinforce the intercostal branch of the nerve, it may 
send one branch to the intercostal portion and another to the part of the nerve joining 
the brachial plexus, or it may consist of a nerve proceeding solely to join the brachial 
plexus by a junction in the first intercostal space with the part of the first thoracic 
nerve, which is engaged in forming the plexus. 
The second thoracic nerve is of large size, though much smaller than the 
first. It passes forwards in the second intercostal space, lying at first in the sub- 
costal groove between the external and internal intercostal muscles. At the level 
of the mid-axillary line it gives off a large lateral branch; continuing its course 
it pierces the internal intercostal muscle and lies upon the pleura; finally, at the 
oS) 
2) 
a 
i — es 
