282 PRACTICAL ANATOMY. 



anterior primary divisions. This must now be located on the ala of the sacrum 

 as it passes down into the pelvis, and its union with the first, second, and third 

 sacral nerves carefully shown. 



2. Muscular brandies to the pyriformis, the quadratus femoris, the gemellus 

 superior, the gemellus inferior, and the obturator interims muscles. Notice ! 

 You will find the branch to the obturator internus, leaving the pelvis by the 

 greater and reentering by the lesser sacro-sciatic foramen. When you dissect 

 the structures in the lesser sacro-sciatic foramen, you will find this nerve with the 

 internal pudic structures. The nerve to the quadratus femoris and gemellus 

 inferior leaves the pelvis by the greater sacro-sciatic foramen, and supplies a 

 branch to the hip-joint as well. 



. You will trace the superior gluteai nerve through the greater sacro-sciatic 

 foramen, above the pyriformis muscle, to the gluteus medius, gluteus minimus, 

 and tensor vaginae femoris. The skin covering these muscles is not sup- 

 plied by this nerve -trunk apparently, but by the ilio-hypogastric and lumbar 

 cutaneous branches from posterior primary divisions. Now, let me impress 

 on the student this fact : A nerve-trunk supplying a muscle must supply the 

 skin covering the muscle, or the serous membrane under the muscle, it 

 any serous membrane be present, and the joint moved by the muscle. The 

 skin branches, in the majority of cases, are given off directly from the nerve- 

 trunk, and are easily found. In a minority of cases, however, the skin branch is 

 not given off directly, but comes from apparently another source ; to such cases as 

 these I see no impropriety in applying the terms divorced, dismembered, or erratic. 

 Confirmatory instances of divorced skin branches are to be found in the small 

 sciatic, the dismembered cutaneous branch of the great sciatic, supplying the 

 skin covering the muscles supplied with motion by the great sciatic nerve ; in the 

 external cutaneous nerve, on the outer part of the thigh, this nerve being divorced 

 from its parent stem, the anterior crural ; in the long pudendal nerve, or nerve of 

 Soemmering, the dismembered branch of the internal pudic nerve, following, in- 

 deed, a most erratic course, ensconced in the sheath of the small sciatic nerve ; 

 in the descendens hypoglossi, a divorced branch of the cervical plexus. In view 

 of the occurrence of anomalies, then, you are to ask yourselves, when dissecting 

 mixed nerves : Have I found (i) muscular branches, (2) cutaneous branches, (3) 

 articular branches ? and (4) are the cutaneous branches direct descendants of tin 

 nerve -trunk, or are they divorced therefrom ? 



3. The inferior gluten! nerve leaves the pelvis by the greater sacro-sciati( 

 foramen below the pyriformis muscle and supplies the gluteus maximus. 



4. The perforating cutaneous nerve will be found when you dissect the 

 region, coming through the greater sacro-sciatic ligament to supply the skin ii 

 this region. 



5. The internal pudic nerve is remarkable for the great number of important 

 areas in which it and its branches are found. It leaves the pelvis by the greater 

 sacro-sciatic foramen below the pyriformis muscle, crosses the ischial spine, reen- 

 ters the pelvis by the lesser sacro-sciatic foramen, here enters Alcock's canal, 

 in the outer \vall of the ischio-rectal fossa, then pierces the triangular ligament, 

 passes through the deep perineal space, again pierces the triangular ligament, 

 passes through the suspensory ligament of the penis to gain the dorsum of this 

 organ. In its course 'it throws off the following branches : As the nerve is 

 entering the canal Alcock's it gives off the inferior lieinorrlioulal and tin 

 prrincal branches. These pass through the fat-bearing ischio-rectal fossa. Th< 

 inferior hemorrhoidal nerve is distributed to the external sphincter ani mnsclt 

 and the skin covering the same. The perineal branch is distributed to the accele- 

 rator tirin;e, transvcrsus perin.ei. erector penis, levator ani, compressor urethra, 

 and to the skin covering the scrotum and petineum. The internal pudic nerve 



