530 



DISSECTION OF THE BACK. 



they divide 

 into two 

 except first. 



External 

 branches 

 are small. 



Internal 

 branches : 



some give 

 cutaneous 

 offsets. 



Second 

 ascends to 



Third 

 supplies 

 neck and 



First nerve 



ends in 

 muscles. 



Dorsal 

 nerves. 



Outer 



branches to 

 erector 

 spinae : 



lower ones 



become 



cutaneous. 



Inner 



branches to 

 tran sverso- 

 spinales : 



upper ones 



reach 



surface. 



arches of the atlas and axis, appear above those arches. All, except 

 the first, divide into internal and external branches. 



The external branches are very small, and end in the splenius, 

 and in the muscles prolonged from the erector spinse. 



The internal branches (tig. 192) are larger than the external ; 

 they are directed towards the spinous processes, the lower three 

 passing beneath the semispinalis, and the upper four over that, 

 muscle. By the side of the spines cutaneous .branches are furnished 

 to the neck and the head from the nerves that are superficial to the 

 semispinalis : these cutaneous offsets ascend to the surface through 

 the splenius, the complexus, and the trapezius muscles, and are 

 distributed as already seen (p. 520). In their course the nerves 

 supply the surrounding muscles, viz., complexus, semispinalis, 

 multifidus spinse, and interspinales. 



The cutaneous branches of the second and third nerves reach the 

 head, and require a separate notice. 



That of the second nerve (fig. 192, 2 ) named great occipital, appears 

 beneath the inferior oblique muscle, to which it gives offsets, and is 

 directed upwards through the complexus and trapezius to end over 

 the occiput (p. 506). 



The branch of the third nerve (fig. 192, 3 ), becoming superficial 

 near the middle line, gives an offset upwards to the lower part of 

 the occiput, internal to the preceding. This nerve usually joins 

 the great occipital twice, viz., beneath the complexus and superficial 

 to the trapezius. 



The posterior primary division of the suboccipital or first spinal 

 nerve (fig. 192, 1 ) is very short, and appears in the interval between 

 the recti and obliqui muscles. In passing from the spinal canal it is 

 placed between the posterior arch of the atlas and the vertebral artery. 

 From its extremity branches radiate to the surrounding muscles, 

 viz., one to the upper part of the complexus, another to the rectus 

 posticus major and minor, and two short branches to the obliquus 

 superior and inferior: the offset to the last muscle joins the inner 

 branch of the second cervical nerve. Occasionally the first nerve 

 gives a cutaneous branch to the occiput. 



IN THE DORSAL REGION. The posterior primary divisions of 

 the dorsal nerves, twelve in number, appear between the transverse 

 processes, and bifurcate into internal and external branches. 



The external branches increase in size from above downwards, 

 and pass beneath the longissimus dorsi to the interval between that 

 muscle and the ilio-costalis, distributing offsets to the several 

 divisions of the erector spinse. The branches of the upper six or 

 seven nerves end in these muscles ; but the lower five or six, after 

 reaching the interval between the longissimus and ilio-costalis, are 

 continued to the surface through the serratus and latissimus 

 muscles, nearly in a line with the angles of the ribs. 



The internal branches are larger above than below, and supply 

 the trans verso-spin ales muscles. The upper six or seven are directed 

 inwards between the semispinalis and multifidus spinse, and become 

 cutaneous by the side of the spinous processes, after perforating the 



