the Lumbo- Sacral Plexus of Macacus rhesus. 271 



spring from one side of it, and the nerve trunks derived from these nerve roots. 

 The 5th lumbar root sends a branch to the sciatic nerve in this type of plexus, and 

 both the obturator and anterior crural nerves are derived from the 4th and 5th 

 lumbar roots. The branch which appears to spring from the 3rd lumbar root, and 

 to pass to the 4th lumbar root, in the figure, is in reality a branch which has its 

 origin from the 4th lumbar root, and which, together with the 3rd lumbar root, 

 forms the external cutaneous nerve. 



Sp.C. = Spinal cord. 

 I.L. = 1st lumbar nerve root. 

 I.S. = 1st sacral nerve root. 

 E.G. = External cutaneous nerve. 

 A.C. = Anterior crural nerve. 

 Obt. = Obturator nerve. 

 Sc. = Sciatic nerve. 



Sc/ = Division of sciatic nerve which supplies the hamstring 

 muscles. 



FIG. 2. From a photograph of the type of lumbo-sacral plexus which is the 

 most common variation met with in Macacus rhesus. The lumbo-sacral cord is re- 

 presented with the nerve roots which arise from one side of it and the nerve trunks 

 which have their origin from these nerve roots. The 5th lumbar root does not send 

 a branch to the sciatic nerve, nor does the 2nd sacral nerve root do so. The 

 obturator nerve receives a slender branch from the 6th lumbar root in addition to 

 those derived from the 4th and 5th lumbar roots. The anterior crural nerve is 

 formed from the 4th and 5th lumbar roots, while the external cutaneous is formed 

 from the 3rd and 4th lumbar roots ; and the 4th lumbar root receives a branch 

 from the 3rd lumbar root, before it gives off any of its own branches. 



Sp.C. = Spinal cord. 



I.L. = 1st lumbar nerve root. 



I.S. = 1st sacral nerve root. 



E.G. = External cutaneous nerve. 



A.C. = Anterior crural nerve. 



Obt. = Obturator nerve. 



Sc. = Sciatic nerve. 



FIG. 3. From a photograph of a lumbo-sacral plexus of Macacus rhesus of the 

 same type as the last, intended to show how in some instances the 2nd sacral nerve 

 root might be erroneously supposed to send a branch to the sciatic nerve, a fallacy 

 which can only be avoided by more minute dissection. 



Sp.C. = Spinal cord. 



ILL. = 2nd lumbar nerve root. 



I.S. = 1st eacral nerve root. 



E.G. = External cutaneous nerve. 



A.C. = Anterior crural nerve. 



Obt. = Obturator nerve. 



Sc. = Sciatic nerve. 



Sc/ = Division of sciatic nerve which supplies the hamstring 

 muscles. 



FIG. 4. From another photograph of the most common type of lumbo-sacral 

 plexus met with in Macacus rhesus, chiefly meant to show how slender the branch 

 from the 5th to the 6th lumbar nerve root is in some cases. 



