532 DR. J. MUKIE ON THE ANATOMY OF THE SEA-LION. 



c. Of Loins and Hind Limb. — Lumbar plexus. Hidden entirely by the psoas muscle 

 and not lying upon but issuing from behind the quadratus lumborum, the lumbar 

 nerves partly are superimposed and partly dip beneath the iliacus, but, relatively to the 

 sacral nerves, are small. 



The external cutaneous nerve sends filaments to the rectus femoris, vastus internus, 

 and crureus, and passes down transversely over the thigh ; superficial to the pectineus 

 and adductors longus and magnus it is distributed to the fascia and skin at the middle 

 and inner side of the shaft of the tibia. 



The muscular branches of the femoral nerve in the groin are distributed to the 

 crureus, vastus internus, and both divisious of the adductor longus and magnus. The 

 femoral nerve accompanies the artery through the opening in the adductor magnus 

 muscle. With regard to the obturator nerve, I include it with the sacral plexus, to 

 which in this case it more properly belongs. 



Sacral Plexus. — This (with junction to lumbo-sacral) is composed of three large 

 trunks, which emerge from as many of the anterior sacral foramina. The first of these 

 trunks immediately on its exit sends off a branch which joins the posterior deep nerves ; 

 the main trunk then goes backwards to opposite the next sacral foramen, where it 

 splits into two nearly equal-sized branches: the shorter one (02 inch) unites with the 

 second sacral nerve ; the longer one forms the obturator nerve, which proceeds under 

 cover of the pelvic fascia to the anterior border of the obturator internus, and pierces 

 it. The second sacral nerve is rather thicker than the first ; it unites with the third 

 at the narrow portion of the pelvis, and there forms a thick single trunk, which passes 

 through the great ischiatic notch. From each sacral nerve a small branch is sent 

 inwards and backwards, which communicates through a ganglion impar with a twig 

 from the sympathetic sacral nerves. The nerve is continued backwards from the gan- 

 glion, and, with the other minute caudal twigs, supplies the muscles and viscera within 

 the pelvis. 



As the sacral plexus passes round and out of the great ischiatic foramen (here consi- 

 derably narrowed) it bears relation to the parts as follows : — From within outwards it 

 lies upon the gemellus inferior, the hinder part of the quadratus femoris, the long 

 adductors and the semimembranosus. Above or dorsally it is covered by the levator 

 cauda? externus, the first and the second portions of the gluteus maximus, the sacro- 

 peronaeus muscle, and the broad biceps. The gluteal artery and vein, as usual, accom- 

 pany the nervous plexus. 



The lesser ischiatic nerve comes off at the outer border of the quadratus femoris, 

 after traversing the great sacro-ischiatic notch with the great ischiatic nerve and vessels. 

 It afterwards lies on the semitendinosus and on the surface of the soleus, being covered 

 by the semimembranosus, the sacro-peronieus, and second portion of the biceps. It 

 proceeds as far as the heel. 



The external popliteal or peroneal nerve proceeds in a slanting manner outwards and 



