ANTERIOR PRIMARY DIVISIONS 973 



3. Lumbar Nerves 



The medial branches of the posterior primary divisions of all the lumbar 

 nerves end in the multifidus spinae and those of the three lower nerves send very 

 small branches to the skin of the sacral region. 



The lateral branches of the upper three nerves pass obliquely lateralward, 

 supplying twigs to the adjacent muscles, pierce the posterior layer of the lumbar 

 aponeurosis at the lateral border of the sacro-spinahs (erector spinse) and enter 

 the subcutaneous tissue. They are, for the most part, cutaneous, forming the 

 superior clunial nerves, which cross the crest of the ilium and pass downward to 

 occupy different planes in the thick superficial fascia which covers the upper part 

 of the gluteus medius. 



The branch from the first lumbar nerve is comparatively smaU, and occupies the most super- 

 ficial plane. The second occupies an intermediate position. The lateral branch from the third 

 nerve is the largest of the three, and occupies the lowest position; it distributes branches over 

 the gluteus maximus as far as the great trochanter. The three nerves anastomose with one 

 another and also with the cutaneous branches from the posterior primary divisions of the two 

 upper sacral nerves. 



The lateral branch of the fourth lumbar nerve is of small size and ends in the 

 lower part of the sacro-spinalis (erector spinse). That of the fifth lumbar is 

 distributed to the sacro-spinalis and communicates with the first sacral nerve. 



4. Sacral Nerves 



The posterior primary divisions of the upper four sacral nerves escape from the 

 vertebral canal by passing through the posterior sacral foramina; those of the 

 fifth sacral nerve pass out through the hiatus sacralis between the posterior sacro- 

 coccygeal ligaments. Those of the upper three sacral nerves divide in the ordi- 

 nary manner into medial and lateral branches. Those of the lower two sacral 

 nerves remain undivided. 



The medial branches of the upper three sacral nerves are of small size, and are 

 distributed to the multifidus spinse. The lateral branches anastomose with one 

 another and with the lateral branch of the last lumbar nerve, forming loops on 

 the posterior surface of the sacrum from which branches proceed to the posterior 

 surface of the sacro-tuberous (great sacro-sciatic) Hgament, where they anasto- 

 mose and form a second series of loops, from which loops two or three branches are 

 given off. These branches pierce the gluteus maximus and come to the surface 

 of that muscle in a line between the posterior superior spine of the ilium and 

 the tip of the coccyx. Then, as the middle clunial nerves, they are distributed 

 to the integument over the medial part of the gluteus maximus, and communi- 

 cate, in their course through the superficial fascia, with the posterior branches 

 of the lumbar nerves. 



The posterior divisions of the lower two sacral nerves unite with one another, 

 with the posterior branch of the third sacral, and with the coccygeal nerve, form- 

 ing loops from which twigs pass to the integument over the lower end of the 

 coccyx. 



The posterior primary division of the coccygeal nerve is also undivided. It 

 separates from the anterior division in the sacral canal and emerges through the 

 hiatus sacralis, pierces the ligaments which close the lower part of that canal, 

 receives a communication from the posterior division of the last sacral nerve, and 

 ends in the skin over the dorsal aspect of the coccyx. 



B. ANTERIOR PRIMARY DIVISIONS 



The anterior primary divisions of the spinal nerves are larger than the pos- 

 terior primary divisions, and each is joined near its origin by a grey ramus commu- 

 nicans from the sympathetic ganghated cord (figs. 751, 752, 762). Beginning with 

 the first or second thoracic nerve and ending with the second or third lumber 

 nerve, each anterior division sends to the gangliated cord a white ramus communi- 

 cans. The same is true of the second and third or of the third and fourth sacral 

 nerves. These white rami are appropriately designated^the visceral branches of 



