140 MERISTIC VARIATION. [part i. 



suggests that the variation of the vertebral regions goes hand 

 in hand with that of the plexus, and though a comparison be- 

 tween Rosenberg's abnormal Chimpanzee with that dissected by 

 Champneys largely bears out this suggestion, yet it is also clear 

 that this correlation is not a precise one, as indeed has already 

 appeared in several instances. 



In giving the compositions of the several nerves of the lumbo- 

 sacral plexus in Man and Chimpanzee, I have given the num- 

 bers of the nerves in the whole series for simplicity of comparison. 

 It will be remembered that a Chimpanzee has one pair of ribs 

 more than Man, the XXIst nerve is the 1st lumbar in Man, but 

 is the 18th dorsal in Chimpanzee, the XXVIth nerve being the 

 1st sacral in both forms. The table given shews, as Champneys 

 sa}<s, that the general arrangement of the nerves of the lower 

 limb and lumbar and sacral plexuses was in Chimpanzee very 

 similar to that in Man, but that the nerves are very differently 

 composed. 



MAN. CHIMPANZEE. 



Ilio-hypogastric} XXI XXL 



llio-mguinal J 



Genito-crural XXI. — XXII XXI. 



External cutaneous XXII. XXIII XXI., XXII. 



Obturator XXIII. XXIV XXL— XXIII. 



Anterior crural XXII.— XXIV XXL— XXIV. 



Superior gluteal XXIV.— XXVI XXIV.— XXVI. 



Sacral plexus XXIV.— XXIX XXIL— XX VII. 



Small sciatic XXIV.— XXIX XXI V.— XX VI. 



(From Champneys, I.e. p. 210.) 



The origin of the nerves is therefore in several cases lower 

 in Man than in the Chimpanzee, although in the absence of ribs 

 on the 20th vertebra Man shews a character which, as compared 

 with the presence of ribs in this position in the Chimpanzee repre- 

 sents a backward Homceosis. 



Man. With the foregoing, compare the case mentioned above 

 (No. 32) in which two entire lumbar nerves joined the sacral 

 plexus in a human subject having no ribs on the 19th vertebra, 

 &c. Struthers, J. Anat. Phys., 1875, p. 72 and p. 29. 



72. For information as to the variations of the lumbo-sacral plexus in 

 the Primates see also Rosenberg, Morph. Jahrb., i. 1876, p. 1-47 et seqq.; 

 and as to cases in Primates and in other vertebrates compare vox 

 Jhering, Das peripherische Nervensystem tier Wirbelthiere, <tc, Leipzig, 

 1878. Of these, two cases of partial backward Homceosis in the 

 lumbo-sacral plexus of the Dog are perhaps noteworthy, as being 

 represented and described in greater detail than many of von Jhering's 

 cases. In one of these the rib of the 13th dorsal (20th vertebra) was 

 not developed, this vertebra being formed as a lumbar and thus itself 

 shewing a backward Homceosis in correlation to that of the nerves 



