284 PRACTICAL ANATOMY. 



3. ll'it/i "i.{.'hat docs the lumbar plexus communicate? 



(i) With the twelfth thoracic nerve, by a brunch named the dor.si lumbar ; (2) 

 with the sacral plexus, by a branch called the lumbo-sacrul cord ; (3) with the 

 lumbar part of the gangliated cord, by branches called rami communicantes. 



4. Describe the syinpatlictic connection, and tell lun^ to conduct a dissection of the 

 same in tins region. 



The lumbar part of the gangliated cord is quite easily found ; the communi- 

 cations with the anterior primary divisions of the lumbar nerves are not difficult 

 to trace out. The double chain of the sympathetic cord consists of four ganglia 

 on each side ; these ganglia are : (i) Right, which lie behind the ascending vena 

 cava ; (2) left, which lie behind and slightly external to the aorta. Find the cord 

 communicating above with the thoracic, and below with the pelvic portion, by 

 continuity. The rami communicantes are quite long in this region ; as a rule, 

 they are two in number, and they accompany the lumbar arteries. The lumbar 

 arteries, then, are your guide in tracing the relation between the lumbar plexus of 

 somatic nerves, and the lumbar part of the sympathetic gangliated cord. 



5. Name the brandies of the lumbar plexus. 



The ilio-hypogastric, ilio-inguinal, genito-crural, external cutaneous, anterior 

 crural, obturator, accessory obturator, muscular branches to the psoas magnus 

 and quadratus lumborum, and the lumbar element of the lumbo-sacral cord. 



6. Give formation and location of tlic lumbo-sacral cord. 



It is formed by the union of the fifth lumbar nerve and a part of the fourth. 

 In practical anatomy you find it buried, in a considerable quantity of fatty con- 

 nective tissue behind the peritoneum, on the ala of the sacrum. This cord gives 

 origin to the superior gluteal nerve, described previously. 



7. Describe the genito-crural nerve, and give its practical importance in 

 diagnosis. 



The nerve arises from the first and second lumbar nerves. It lies on the psoas 

 magnus muscle in the lower part of its course. It divides into: (i) A genital 

 branch, which follows the spermatic vessels and supplies the cremaster muscle 

 with motion. In practical anatomy you find this branch behind the spermatic cord. 

 (2) A cutaneous branch, the crural, which is distributed to the skin of the upper 

 inner part of the thigh. The cremasteric reflex depends on this nerve. Irritate 

 the skin of the thigh corresponding to the sensory distribution of this, the genito- 

 crural nerve, and the testicle of the corresponding side will be elevated by the 

 contraction of the cremaster muscle. In diagnosis, the movement of the testicle 

 thus produced argues in favor of the integrity of the spinal cord between the first 

 and second lumbar nerves. In the female this nerve is rudimentary, and, there 

 being no cremaster in this sex, the genital branch of the nerve is distributed to 

 the round ligament of the uterus ; the crural branch is distributed as in the male. 

 The reflex phenomena in the female are recorded as a twitching of the external 

 oblique ; still, I think careful observation would prove such record erroneous. 1 he 

 twitching must be in the round ligament of the uterus, since this is the homo- 

 logue of the spermatic cord. 



8. Describe a patcllar reflex circuit and give its importance in diagnosis. 



The anterior crural nerve is concerned in this reflex. Sensory branches from 

 this nerve, distributed over the insertion of the quadriceps, forming the plexus 

 patellae, convey sensation to a transfer centre ; and motor branches from the 

 anterior crural induce contraction of the extensor group of muscles on the front 

 of the thigh. This reflex movement is normal in health. It is absent in loco- 

 motor ataxia and in the case of lesions and diseases affecting the anterior gray 

 cornua of the spinal cord. It is increased after epileptic seizures, in spinal irrit- 

 ability, tumors of the brain and diseases of the lateral tracts of the cord, and in 

 lateral and cerebro-spinal sclerosis. 



