IV. OF RAN A PIPIENS. 45 



X. Coccygeal Nerve ; 10. This is the last of the series of spinal nerves, and 

 from its minuteness does not appear to have attracted notice ; consequently, the 

 number of pairs is usually enumerated as nine. It is most easily detected on 

 either side of the coccyx beneath the muscles extending from it to the ilia. If 

 traced from its termination towards the chord, it will be found entering the 

 cavity of the coccyx by a foramen pierced quite obliquely in its walls at a short 

 distance from the anterior extremity of the bone. This nerve is attached to the 

 chord by both kinds of roots, just beyond the third crural or ninth pair of spinal 

 nerves. The detection of this nerve has especial interest, since it demonstrates 

 conclusively the homology of the anomalous-shaped coccyx with a true vertebra, 

 and also makes the number of nerves and vertebral pieces equal. 



Cutaneous Branches of the Spinal Nerves. The skin of Frogs, it will be remem- 

 bered, is attached only to a very limited extent to the parts beneath, so that there is 

 a series of large subcutaneous cavities, which are for the most part separated from 

 each other. The first or dorsal subcutaneous cavity covers the whole region of the 

 back, extending from the occiput to the posterior part of the trunk, and limited on 

 the sides by the union of the skin with the muscles beneath, on a line extending 

 from behind the eyes as far as the pelvis. The lateral cavities, one on each flank, 

 are limited by the lines described above, and two others, one on each side, extending 

 from the axilla to the pelvis. The fourth or abdominal cavity is comprised be- 

 tween the two last, and extends over the whole abdominal region. 



The cutaneous nerves escape through the muscles to the -skin, mainly in three 

 directions ; namely, on each side of the median line on the back, and at the upper 

 and lower lines which limit the lateral subcutaneous cavities. The dorsal branches 

 are in pairs, nine in number, and corresponding with the first nine vertebra?. In 

 front of the scapula is a minute branch of this series, which is derived from the 

 hypoglossus, and to this same series should be added the cutaneous filament from 

 the vagus distributed to the skin near the occiput. On the upper lateral line eight 

 pairs are given to the skin ; on the sides in the lateral cavity five pairs descend to 

 the lower lateral line, where, with three others given eff more posteriorly, they 

 enter the skin. These last branches seem to be the ones liable to the greatest irreg- 

 ularity. The existence of a dorsal cutaneous branch from the vagus and hypoglos- 

 sus both, added to the facts already stated under another head, go still further to 

 show their identity with common spinal nerves. 



Crystal Capsules attached to the Spinal Nerves. (Plate I. Fig. 1, i, i.) The exist- 

 ence of certain white bodies on either side of the vertebral column in Frogs seems 

 for a long time to have attracted attention. They are referred to by Blasius, in his 

 Anatome Animalium,* and are figured by Swann,j- though he gives no descriptions. 

 Wagner mentions them as follows : " The ganglia admit of being very readily 



* " Ab utraque spinalis medullas parte, substantia qua?dam albicans calcis instar adhaerescit, quam vasa 

 plurima perreptant ; substantia hacc sail volatili est analoga, cum ex observatione Swammerdammii 

 affuso spirito acido effervescat. Cui usui tot vasorum plexibus inserviat admodum obscurum est." 

 Gerardi Blasii Anatome Animalium, Amstellodami, 1681, p. 291. 



t Comp. Anat. Nerv. Syst., Plate VII. Figs. 5, 6. 



7 



