I320 HUMAN ANATOMY. 



Variations. — That portion of the fourth lumbar nerve, or 7t. fur caHs, which joins the lumbo- 

 sacral cord, is usually less than half of the parent trunk, but varies from one-twentieth to 

 nine-tenths. When large, it may be joined by a branch from the third lumbar, and when 

 small the fifth lumbar may contribute to the lumbar plexus, the fibres going to the ante- 

 rior crural alone or to the anterior crural and obturator nerves. The branch to the lumbo- 

 sacral cord from the fourth lumbar may be absent and in such an event the fifth is the only 

 furcal nerve sending fibres to both the lumbar and the sacral plexus. It is thus possible to 

 have as furcal nerves the third and fourth, the fourth alone, the fourth and fifth or the fifth 

 alone, and according to the high or low position of these there is found a corresponding origin 

 of the branches of the lumbar plexus. In this manner are accounted for the high and low, or 

 prefixed and postfixed types of plexus. 



Branches of the lumbar plexus are : 



1. The Muscular 5. The External Cutaneous 



2. The Ilio-Hypogastric 6, The Obturator 



3. The Ilio-Inguinal 7. The Accessory Obturator 



4. The Genito-Crural 8.^ The Anterior Crural 



I. The Muscular Branches. 



The muscular branches (rr. musculares) supply the quadratus lumborum, the 

 psoas magnus and the psoas parvus. 



The branches to the quadratus lumborum arise from the upper three or four 

 iumbar nerves, and sometimes from the last thoracic, and pass directly into the 

 quadratus. 



The branches to \X\& psoas magnus arise mainly from the second and third lumbar 

 nerves, there sometimes being additional ones from the first and fourth. They pass 

 directly into the muscle. 



The branches to the psoas parvus consist of filaments from the first or second 

 lumbar nerve which reach the muscle by piercing the underlying psoas magnus. 



2. The Ilio-Hypogastric Nerve. 



• 



The ilio-hypogastric nerve (n. iliohypogastricus) (Fig. 1107) is the uppermost 



branch of the plexus and is somewhat larger than its associate, the ilio-inguinal. Whilst 



it derives the major portion and sometimes all of its fibres from the first lumbar nerve, 



it usually receives others from the twelfth and occasionally the eleventh thoracic. It 



emerges from the lateral margin of the upper portion of the psoas magnus and runs, 



below and parallel with the twelfth thoracic nerve, outward and downward, posterior 



to the kidney and anterior to the quadratus lumborum. Reaching the crest of the 



ilium, it pierces the transversalis muscle and occupies the intermuscular space between 



the internal oblique and the transversalis. After coursing along this interval as far 



as the middle of the iliac crest, it divides into its terminal branches, (a) the iliac and 



{b') the hypogastric, which correspond morphologically with the lateral and anterior 



cutaneous branches of the thoracic nerves. There are also some (r) muscular 



branches. 



a. The iliac branch (r. cutaneus lateralis) pierces the internal and external obliques about 

 the middle of the iliac crest and is distributed to the integument of the anterior gluteal region 

 which covers the gluteus medius and the tensor fasciae femoris (Fig. 1083). It forms an 

 inosculation with the lateral cutaneous branch of the twelfth thoracic nerve and maintains an 

 even balance with it, deficiency in the development of either being recompensed for by a com- 

 pensating increase in size of the other. 



b. The hypogastric branch (r. cutaneus anterior) continues the direction and course 

 of the main trunk between the transversalis and the internal oblique almost to the linea alba. 

 Near the anterior superior spine of the ilium it forms an inosculation with the ilio-inguinal 

 nerve. As it approaches the region of the internal abdominal ring it begins to push its way 

 gradually through the internal oblicjue and gain the interval between the internal and the exter- 

 nal oblique (Fig. 1105). A short distance superior and internal to the external abdorninal ring 

 it traverses a tiny foramen in the aponeurosis of the external oblique and breaks up into fibres 

 of termination which supply the integument of the suprapubic region. 



c. Muscular branches (rr. musculares) arise from the hypogastric branch in its course 

 through the abdominal wall and supply the transversalis, the internal oblique and the external 

 oblique. 



