THORACIC NERVES 9.71 



1. Cervical Nerves 



The posterior primary division of the first cervical or sub -occipital nerve 

 springs from the trunk, between the vertebral artery and the posterior arch of 

 the atlas, passes dorsalward into the sub-occipital triangle, and breaks up into 

 branches which supply the superior oblique, the inferior oblique, and the major 

 rectus capitis posterior muscles, which form the lateral boundaries of the triangle. 

 It also gives a branch across the posterior surface of the major rectus capitis pos- 

 terior to the minor rectus capitis posterior, and a branch to the semispinalis 

 capitis (complexus) in the roof of the triangle. 



It communicates with the medial branch of the posterior primary division of the second 

 cervical nerve, either through or over the inferior obhque muscle, and it occasionally gives a 

 cutaneous branch to the skin of the upper part of the back of the neck and the lower part of 

 the scalp. 



The posterior primary division of the second cervical nerve is the largest pos- 

 terior division of all the cervical nerves. It divides into a small lateral branch and 

 a very large medial branch. The lateral branch gives a twig to the inferior oblique 

 and terminates in branches which supply the splenius and longissimus capitis 

 (trachelo-mastoid) muscles. The medial branch is the greater occipital nerve. 

 It turns around the lower border of the inferior oblique, crosses the sub-occipital 

 triangle obliquely, pierces the semispinalis capitis (complexus), the tendon of the 

 trapezius, and the deep cervical fascia, passing through the latter immediately 

 below the superior nuchal line of the occipital bone, and it divides into several 

 terminal sensory branches which ramify in the superficial fascia of the scalp. 



It gives one or two motor twigs to the semispinalis capitis (complexus), and its terminal 

 branches which are accompanied by branches of the occipital artery supply the skin of the scalp, 

 above the superior nuchal line, as far forward as the vertex. Occasionally one branch reaches 

 the pinna and supplies the skin on the upper part of its medial aspect. As it turns around the 

 inferior oblique it gives branches which join with the medial branches of the posterior primary 

 divisions of the first and third cervical nerves, and in this manner a small looped plexus is formed 

 beneath the semispinalis capitis (complexus) muscle, the posterior cervical plexus of Cruveilhier. 



The posterior primary branches of the third, fourth, and fifth cervical nerves 



divide at the lateral border of the semispinalis colli into medial and lateral branches. 

 The medial branches of the third, fourth, and fifth nerves run backward between 

 the semispinalis colli and capitis (complexus), supplying both muscles. Then, 

 after passing backward between the semispinalis capitis and the ligamentum 

 nuchse, the^^ pierce the origin of the trapezius and supply the skin of the back of 

 the neck. The greater part of the medial branch of the third nerve, which runs 

 upward in the superficial fascia to the scalp, is called the third or smallest occipital 

 nerve ; it interlaces with the greater occipital nerve, and it supplies the skin of the 

 upper part of the back of the neck, near the middle line, and the skin of the 

 scalp in the region of the external occipital protuberance. 



The medial branches of the posterior primary divisions of the sixth, seventh, 

 and eighth cervical nerves pass to the median side of the semispinalis colli, between 

 it and the subjacent multifidus spinas, and they end in the neighbouring muscles. 

 The lateral branches of the posterior primary divisions of the last five cervical 

 nerves are small and they are distributed to the longissimus capitis (trachelo- 

 mastoid), the ilJo-costalis cervicis (cervicalis ascendens), the longissimus cervicis 

 (transversalis cervicis), the semispinalis capitis (complexus), and the splenius 

 muscles. 



2. Thoracic Nerves 



The posterior primary divisions of all the thoracic nerves divide into medial 

 and lateral branches while in the vertebral groove. The medial branches of the 

 upper six thoracic nerves pass dorsalward between the semispinalis clorsi and the 

 multifidus spinse; they supply the spinalis dorsi, the semispinahs dorsi, the multi- 

 fidus spinse, the rotatores spinse, the intertransversales, and the interspinals 

 muscles; and they end in cutaneous branches which, after piercing the trapezius, 

 turn lateralward in the superficial fascia of the back, and suppty the skin as far as 

 the middle of the scapula. The cutaneous branch of the second nerve is the larg- 

 est; it can be traced lateralward as far as the acromion process. The medial 

 branches of the lower six thoracic nerves run dorsalward, between the longissi- 



