rOSTERIOR DIVISIONS OF SPINAL NEEVES. 573 



splenius and complexus have been divided in the neck, and the erectoi- spinre separated 

 and partially removed in the back, so as to expose the deep issue of the nerves. 



a, a, lesser occipital nerve from the cervical plexus ; 1, external muscular branches of 

 the first cervical nerve and union by a loop with the second ; 2, placed on the rectus 

 capitis posticus major, marks the great occipital nerve passing round the short muscles 

 and i^ercing the comjilexus ; the external branch is seen to the outside ; 2', cranial dis- 

 tribution of the great occiintal ; 3, external branlih of the posterior primary division of 

 the third nerve ; 3', its internal branch, or tliird occipital nerve ; 4', 5', 6', 7', 8', 

 internal branches of the several corresponding nerves on the left side ; the external 

 branches of these nerves preceding to muscles are displayed on the right side : d 1 to 

 d 6, and thence to d 12, external muscular branches of the posterior primary divisions of 

 the twelve dorsal nerves on the right side •,dV, to d 6', the internal cutaneous branches 

 of the six upper dorsal nerves on the left side ; d 7' to d 12', cutaneous branches of the 

 six lower dorsal nerves from the external branches ; I, I, external branches of the pos- 

 terior primary branches of several lumbar nerves on the right side piercing the muscles, 

 the lower descending over the gluteal region ; V, V, the same more superficially on the left 

 side ; s, s, on the right side, the issue and union by loops of the posterior primary 

 divisions of four sacral nerves ; s', s', some of these distributed to the skin on the left side. 



A cutaneous hrannli is occasionally given to the back of the head ; it accom- 

 panies the occipital artery, and is connected beneath the integument with the 

 great and small occipital nerves. 



CERvic.\Ti Nerves {excepting tlie snh-occipifal). — The external 

 ■branches ,G;ive only muscular offsets, and are distributed to the splenius 

 and the slender muscles prolonged to the neck from the erector spintB, 

 A'iz., the eervicalis ascendens, and the transversalis colli with the 

 trachelo-mastoid. That of the second nerve is the largest of the 

 series of external branches, and is often united to the corresponding- 

 branch of the third ; it supplies the complexus muscle which covers 

 it, and ends in the splenius and trachelo-mastoid muscles. 



The internal branches, larger than tlie external, are differently 

 disposed at the upper and the lower parts of the neck. That of the 

 second cervical nerve is named, from its size and destination, the great 

 occipital, and requires separate notice. Tlie rest are directed inwards 

 to the spinous processes of the vertebra. Those derived from the third, 

 fourth, and fifth nerves pass over the semispinalis and beneath the 

 complexus muscle, and, having reached the spines of the vertebra, 

 turn transversely outwards and are distributed in the integument over 

 the trapezius muscle. From the cutaneous branch of the third nerve a 

 branch passes upwards to the integument on the lower part of the 

 occiput, lying at the inner side of the great occipital nerve, and is some- 

 times called third occipital nerve. 



Between the inner branches of the first three cei-vical nerves, beneath the 

 complexus, there are frequently communicating fasciculi ; and this communica- 

 tion CruveUhier has designated as '■ the posterior cei-vical plexus.' 



The internal branches from the lowest three cervical nerves are placed 

 beneath the semispinalis muscle, and end in the muscular structure, 

 without furnishing (except occasionally the sixth) any offset to the skin. 

 These three nerves are the smallest of the series. 



The great occijjitcd nerve is directed upwards on the lower oblique 

 muscle, and is transmitted to the surface through the complexus and 

 trapezius muscles, giving twigs to the complexus. Ascending with 

 the occipital artery, it divides into branches which radiate over the 

 occipital part of the occipito-frontalis muscle, some appearing to enter 

 the muscle, and others joining the smaller occipital nerve. 



An avrioilar hranch is sometimes supplied to the back of the ear by tiie great 

 occipital nerve. 



