



THE THORACIC NERVES 923 



The medial branch (ramus medialis; internal branch), called from its size and 

 distribution the greater occipital nerve (n. occipitalis major; great occipital nerve), 

 ascends obliquely between the Obliquus inferior and the Semispinalis capitis, and 

 pierces the latter muscle and the Trapezius near their attachments to the occipital 

 bone (Fig. 801). It is then joined by a filament from the medial branch of the 

 posterior division of the third cervical, and, ascending on the back of the head 

 with the occipital artery, divides into branches which communicate with the lesser 

 occipital nerve and supply the skin of the scalp as far forward as the vertex of the 

 skull. It gives off muscular branches to the Semispinalis capitis, and occasionally 

 a twig to the back of the auricula. The lateral branch (ramus lateralis; external 

 branch) supplies filaments to the Splenius, Longus capitis, and Semispinalis capitis, 

 and is often joined by the corresponding branch of the third cervical. 



The posterior division of the third cervical is intermediate in size between those 

 of the second and fourth. Its medial branch runs between the Semispinalis capitis 

 and cervicis, and, piercing the Splenius and Trapezius, ends in the skin. While 

 under the Trapezius it gives off a branch called the third occipital nerve, which pierces 

 the Trapezius and ends in the skin of the lower part of the back of the head (Fig. 

 801). It lies medial to the greater occipital and communicates with it. The 

 lateral branch often joins that of the second cervical. 



The posterior division of the suboccipital, and the medial branches of the posterior division 

 of the second and third cervical nerves are sometimes joined by communicating loops to form 

 the posterior cervical plexus (Cruveilhier) . 



The posterior divisions of the lower five cervical nerves divide into medial 

 and lateral branches. The medial branches of the fourth and fifth run between the 

 Semispinales cervicis and capitis, and, having reached the spinous processes, 

 pierce the Splenius and Trapezius to end in the skin (Fig. 801). Sometimes the 

 branch of the fifth fails to reach the skin. Those of the lower three nerves are 

 small, and end in the Semispinales cervicis and capitis, Multifidus, and Inter- 

 spinales. The lateral branches of the lower five nerves supply the Iliocostalis 

 cervicis, Longissimus cervicis, and Longissimus capitis. 



The Thoracic Nerves (Nn. Thoracales). 



The medial branches (ramus medialis; internal branch) of the posterior divisions of 

 the upper six thoracic nerves run between the Semispinalis dorsi and Multifidus, 

 which they supply; they then pierce the Rhomboidei and Trapezius, and reach 

 the skin by the sides of the spinous processes (Fig. 801). The medial branches 

 of the lower six are distributed chiefly to the Multifidus and Longissimus dorsi, 

 occasionally they give off filaments to the skin near the middle line. 



The lateral branches (ramus lateralis; external branch) increase in size from above 

 downward. They run through or beneath the Longissimus dorsi to the interval 

 between it and the Iliocostales, and supply these muscles; the lower five or six 

 also give off cutaneous branches which pierce the Serratus posterior inferior and 

 Latissimus dorsi in a line with the angles of the ribs (Fig. 801). The lateral 

 branches of a variable number of the upper thoracic nerves also give filaments 

 to the skin. The lateral branch of the twelfth thoracic, after sending a filament 

 medialward along the iliac crest, passes downward to the skin of the buttock. 



The medial cutaneous branches of the posterior divisions of the thoracic nerves descend for 

 some distance close to the spinous processes before reaching the skin, while the lateral branches 

 travel downward for a considerable distance it may be as much as the breadth of four ribs 

 before they become superficial; the branch from the twelfth thoracic, for instance, reaches the 

 skin only a little way above the iliac crest. 1 



See article by H. M. Johnston, Journal of Anatomy and Physiology, vol. xliii. 



