ANTERIOR PRIMARY DIVISIONS. 635 



fleshy part of the ilio-costalis, and the apcmeurosis of the latissimus dorsi ; 

 they cross the iliac crest near the edge of the erector spinse, 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 in grooves close to the articular 

 processes of the vertebrae, and sink into the mukifidus spinse muscle. 



SACRAL NERVES. The posterior divisions 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 spinre 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 Jirst three sacral nerves are small, and are 

 lost in the multifidus spinse 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 by the gluteus maximus muscle, they 

 form a second series of loops, and end in cutaneous 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 extremity of the sacrum, 

 and the third about midway between the other two. All are directed out- 

 wards over the great gluteal muscle. 



In six dissections by Ellis tliis arrangement was found to be the most frequent. 

 The variations to which it is liable are these : the first nerve may not take part in 

 the second series of loops, and the fourth may be associated with them. 



The posterior divisions of the last two sacral nerves are smaller than those 

 above them, and are not divided into external and internal branches. They 

 are connected with each other by a loop on the back of the sacrum, and the 

 lowest is joined in a similar manner with the coccygeal nerve ; one or two 

 small filaments from these sacral nerves are distributed behind the coccyx. 



COCCYGEAL NERVE. The posterior division of the coccygeal nerve is very 

 small, and separates from the anterior primary portion of the nerve in the 

 sacral canal. It is joined by a communicating filament from the last sacral 

 nerve, and ends in the fibrous structure covering the posterior surface of the 

 coccyx. 



ANTERIOR PRIMARY DIVISIONS 



OP THE SPINAL NERVES. 



The anterior primary divisions of the spinal nerves are distributed to the 

 parts of the body situated in front of the vertebral column, including the 

 limbs. They are, for the most part, ponsiderably larger than the posterior 

 divisions. 



The anterior division of each spinal nerve is connected by one or two 

 slender filaments with the sympathetic. Those of the cervical, lumbar, and 

 sacral nerves form plexuses of various forms ; but those of the dorsal nerves 

 remain for the most part separate one from another. 



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