THE PELVIS. 283 



now continues its course in Alcock's canal, and through the deep triangular peri- 

 neal space, under the name of dorsal nerve of the penis, to which, with the sym- 

 pathetic from the pelvic plexus, it is distributed. 



6. The small sciatic leaves the pelvis by the greater sacro-sciatic foramen 

 below the pyriformis, and breaks up into four principal cutaneous branches 

 ascending, descending, external, and internal. The largest of the internal branches 

 crosses the tuberosity of the ischium, and is distributed to the labia majora under 

 the name of inferior pudendal, or nerve of Soemmering. 



7. The great sciatic nerve takes its name at the lower border of the greater 

 sacro-sciatic foramen, through which you see it leaving the pelvis below the pyri- 

 formis muscle. Examine closely and you can see some very small branches. 

 These are articular to the hip-joint. Lower down are given off muscular branches 

 to the biceps semitendinosus, semimembranosus, and adductor magnus muscles. 

 As a rule, the nerve divides six inches above the knee into the internal and 

 external popliteal nerves. 



Branches of the Internal Popliteal Nerve of Great Sciatic : 



1. The communicans tibialis to the communicans fibularis, a branch of the 

 external popliteal to form by this union the short saphenous nerve. This nerve 

 supplies the skin over the superficial group of muscles of the leg. 



2. Articular- branches to the knee, with the articular arteries, superior and 

 inferior internal, and the azygos. 



3. Muscular branches to the gastrocnemius, soleus, plantaris, and popliteus. 



4. Posterior tibial, which gives off an articular branch to the ankle ; a plantar 

 cutaneous branch to the heel and sole of foot on the inner side ; muscular 

 branches to the flexor longus digitorum, tibialis posticus, flexor longus hallucis ; 

 a communicating branch to the soleus muscle. 



5. The internal plantar, which gives off articular branches to the tarsus and 

 metatarsus, digital cutaneous branches to the four lesser toes, muscular branches 

 to the abductor hallucis, flexor brevis digitorum, flexor brevis hallucis, and the 

 two tibial lumbricales. 



6. Extei'nal plantar, that supplies one and one-half toes cutaneously ; mus- 

 cular branches to flexor accessorius, abductor minimi digiti, the two outer lumbri- 

 cales, the adductor hallucis obliquus, the adductor hallucis transversus, the 

 flexor brevis minimi digiti, and all the interossei muscles. 



Branches of the External Popliteal of Great Sciatic : 



1. The communicans fibularis to the communicans tibialis to form the short 

 saphenous nerve. 



2. Three articular branches to the knee, proceeding with the superior and 

 inferior external articular arteries and the azygos. 



3. Cutaneous brandies to the skin covering the peronei muscles, being given 

 off with the communicans fibularis. 



4. The anterior tibial nerve, which gives off an articular branch to the ankle, 

 to the metatarso-phalangeal joints of all the toes. Muscular brandies to the 

 tibialis anticus, extensor proprius hallucis, extensor longus digitorum, extensor 

 brevis digitorum, and a muscular branch to the first interosseous muscle. 



5. The musculo-cutancoiis, which gives off its muscular branches to the 

 peroneus longus and peroneus brevis muscles. Cutaneous branches, internal 

 and external, to the dorsum of the foot, communicating with the internal and 

 external saphenous nerves. 



1 . Where is the lumbar plexus located f 



It is behind the peritoneum in the deep substance of the psoas magnus muscle. 



2. How is tlie lumbar plexus formed / 



By the union of the anterior primary divisions of the first, second, third, and 

 a part of the fourth lumbar nerves, and the dorsi-lumbar cord. 



