the Lumbo- Sacral Plexus of Macacus rhesus. 249- 



The similarity between the plexus which I have found most common 

 and the " prefixed " plexus of Sherrington is obvious ; but there is 

 one point of difference. The branch figured by Sherrington as going 

 from the 3rd to the 4th lumbar, and thus taking part in the formation 

 of the anterior crural and obturator nerves, I have not found present. 

 So, too, the variation which I have described as most common agrees 

 with what he calls the " postfixed " type of plexus, with the exception 

 that I have not found a branch from the 6th lumbar to the anterior 

 crural ; nor have I found that the 2nd sacral sends a branch to the 

 sciatic. But the number of times I have met with this form of varia- 

 tion have not been sufficiently frequent to justify my denying the 

 existence of such a branch as that from the 2nd sacral root to the 

 sciatic. Indeed, its existence in some cases is rendered very probable 

 by a comparison of this form of plexus with that most commonly met 

 by me in the dog, which resembles it, and in which the 2nd sacral 

 root sends a branch to the sciatic trunk. It is curious that in the 

 species I have examined, the type of plexus most commonly met with 

 in the dog should form the exception in the monkey, while that most 

 commonly met with in the monkey should be the exception in the 

 dog. The fundamental point of difference in the constitution of the 

 two plexuses in the species I have examined has been the presence of 

 a branch from the 5th to the 6th lumbar root in the one form of 

 plexus, and its absence in the other, and it shows that the passage 

 from the one type of plexus to the other is not an abrupt, but a 

 gradual one, for, while in the majority of monkeys examined I found 

 the branch from the 5th to the 6th lumbar root to be large, all 

 graduations were met with down to the most minute filament con- 

 necting the two roots (see fig. 4). 



The Muscles of the Posterior Extremity of the Monkey, and their Actions.. 



In confirmation of Sherrington I find that the muscles of the 

 posterior extremity of the monkey (Macacus rhesus) resemble very 

 closely those met with in man ; but a few points of difference exist,, 

 and must be briefly alluded to. 



The gluteus maximus is a very thin flat muscle. There is no 

 evidence of the existence of a peroneus tertius; but peroneo-tibialis 

 muscle is sometimes present. The slip which the abductor hallucis 

 in man occasionally sends to the first phalanx of the second digit is 

 very large and constant, forming a separate muscle in fact. 



As was explained in the paper on the brachial plexus of the dog, 

 certain consequences of the action of the muscles deserve careful 

 attention. In studying the mechanism by which the movements are 

 brought about at the various joints, I found that a muscle might 

 bring about a movement at a given joint upon which it has no direct 



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