chap, iv.] spinal nerves: batrachia. 143 



anastomose with the plexus, though it gives off the superior thoracic 

 which in both Nana and Pipa comes off at a point peripheral to the 

 formation of the plexus (Fiirbringer). 



If the two spinal nerves which come out of the urostyle in Pipa 

 may be taken to shew that this bone contains n + 2 vertebrae while the 

 single pair in liana shews the urost3 ? le to consist of n + 1, there is in 

 Pipa (as compared with liana), a diminution of one in the total 

 number of vertebra?, together with a backward Homoeosis, which is 

 seen in the fact that the 8th vertebra bears the pelvic girdle. Turning 

 now to the nervous system, the fact that the last spinal nerves to join 

 the brachial plexus in Pipa are the Illrd, while in liana they are the 

 IVth, is again an evidence of backward Homoeosis. But if this process 

 were completely carried out, the pair of nerves which in Pipa pass out 

 through the 1st vertebra should pass out between this vertebra and the 

 skull, i.e. in the position of the suboccipital of the Urodela. Beyond 

 this analysis cannot be carried, and this case is a good illustration of 

 the fact that the hypothesis of an individual homology between the 

 segments does not satisfy all the conditions of the problem. 



Relation between the ordinal f)osition of spinal nerves and 

 their distribution to the limbs. 



This subject is introduced partly because it further illustrates the 

 nature of the relations which the spinal nerves maintain towards each 

 other, and thus bears indirectly on the phenomena of their Variation ; 

 but chiefly because it presents a view of some of the complexities which 

 arise in the apportionment of organs centrally disposed in Meristic 

 Series, to the parts of peripheral appendages having no clear or co- 

 incident relation to the primary or fundamental segmentation of the 

 body. The facts have thus a value as furnishing a kind of commentary 

 on the nature of Meristic Repetitions in vertebrates. In any attempt 

 to interpret or comprehend Meristic Repetition as a whole, they must 

 be taken into account. 



The principles of the distribution of the spinal nerves to the inuscles 

 of the fore-limb have been thus enuntiated by Herringham. 



1. "Of two muscles, or of two parts of a muscle, that which is 

 nearer the head-end of the body tends to be supplied by the higher, 

 that which is nearer the tail-end by the lower nerve. 



2. "Of two muscles, that which is nearer the long axis of the 

 body tends to be supplied by the higher, that which is nearer the peri- 

 phery by the lower nerve. 



• 3. "Of two muscles, that which is nearer the surface tends to 

 be supplied by the higher, that which is further from it by the lower 

 nerve." Herringham, W. P., Proc. Roy. Soc, xli. 1886, p. 437. 



Details are given shewing the manner in which the innervation of 

 the muscles in Man bears out these principles. 



Forgue and Lannegrace ', who worked, with dogs and monkeys 

 by physiological methods, arrived at conclusions identical with those 

 which Herringham came to by human dissection. 



1 Distrib. des racines matrices, &c, Montpellier, 1883, p. 45 [quoted from 

 Herringham: not seen, W. B.]; also Comptes Eendus, 1884, cxviii. p. 687. 



