574 THE SriXAL NERVES. 



Dorsal Xerves. — The external branches increase in size from 

 above downwards. They are directed through or beneath the longis- 

 simus dorsi to the space between that mnscle and the iho-costalis and 

 accessorius ; they supply both those muscles, together with the small 

 muscles continued upwards from the erector spinte to the neck, and 

 also the levatores costarum. The lower five or six nerves give cuta- 

 neous twigs, which are transmitted to the integument in a line with 

 the angles of the ril)s. 



The internal branches of the upper six dorsal nerves appear in the 

 interval between the multitidus spinaj and the semispinalis dorsi ; they 

 supply those muscles, and become cutaneous by the side of the spinous 

 processes of the vertebro3. The cutaneous branch of the second 

 nerve, and sometimes others, reach as fnv as tlie scapula. The internal 

 branches of the lower six dorsal nerves are placed between the multi- 

 fidus spinas and longissimus dorsi, and end in the multifidus without 

 giving branches to the integument. Where cutaneous nerves are sup- 

 plied by the internal branches, there are none from the external branches 

 of the same nerve, and vice versa. 



Lumbar Nerves. — The external branches enter the erector spin^, 

 and give filaments to the intertransverse muscles. From the upper 

 three, cutaneous nerves are supplied ; and from the last, a fasciculus 

 descends to the corresponding branch of the first sacral nerve. The 

 ciilanroi/s nerves given from the external branches of the first three 

 lumbar nerves, pierce the fleshy part of the ilio-costalis, and the 

 aponeurosis of the latissimus dorsi : they cross the iliac crest near the 

 edge of the erector spin^e, and terminate in the integument of the 

 gluteal region. One or more of the filaments may be traced as far as 

 the great trochanter of the femur. 



The internal branches wind backwards m grooves close to the articu- 

 lar processes of the vertebra?, and sink into the mulifidus spinfe muscle. 



Sacral Nerves. — The posterior division of the nerves, except the 

 last, issue from the sacrum through its posterior foramina. The first 

 three are covered at their exit from the bone by the multifidus spina) 

 muscle, and bifurcate like the posterior trunks of the other spinal 

 nerves ; but the remaining two, which continue below that muscle, 

 have a peculiar arrangement, and require separate examination. 



The internal branches of the first three sacral nerves are small, and 

 are lost in the multifidus spinte muscle. 



The external branches of the same nerves are united with one 

 another, and with the last lumbar and fourth sacral nerves, so as to 

 form a series of anastomotic loops on the upper part of the sacrum. 

 These branches are then directed outwards to the cutaneous or posterior 

 •surface of the great sacro-sciatic ligament, where, covered l\y the gluteus 

 maximus muscle, they form a second series of loops, and end in cuta- 

 neous nerves. These pierce the great gluteus muscle in the direction 

 of a line from the posterior iliac spine to the tip of the coccyx. They 

 are commonly three in number — one is near the innominate bone, 

 another opposite the sacrum, and the third about midway between the 

 other two. All are directed outwards over the great gluteal muscle. 



In six dissections by Ellis this arrangement was found to be the most fre- 

 quent. The variations to which it is liable are these : — the first nerve maj' not 

 take part in the formation of the second series of loops, and the fourth may 

 be associated with them. 



