40 AMPHIBIA. 



each spinal nerve. In the frog, the spinal cord is very short, the nerves of the lower 

 extremities form a long cauda equina; there are anterior and posterior bundles of 

 nerves, each posterior bundle forms a ganglion. 



SPINAL NERVES. In the turtle, the first two cervical nerves, when derived 

 entirely from the anterior bundles, are altogether given to the muscles ; but when the 

 second has a filament from the posterior, a portion of it is likewise given to the skin. 

 The two first, nevertheless, have anterior and posterior trunks like the rest. The 

 anterior trunk of the first gives filaments to the cervical muscles, and joins a branch 

 of the ninth, and then gives filaments to the outside of the carotid artery, and 

 terminates in the sterno-thyroid muscles, and one attached to the back of the 

 oesophagus ; the posterior trunk communicates with the posterior branch of the ninth, 

 and terminates entirely in the muscles at the back of the neck. The anterior trunk 

 of the second passes to a long muscle at the anterior part of the neck, and the 

 posterior to others on the posterior. A branch from the third cervical nerve may be 

 traced through a portion of muscle to the skin of the face, and one from each of those 

 below to the skin of the neck ; the third and fourth also give branches to the muscles 

 of the neck. The fifth, sixth, seventh, and first dorsal form the axillary plexus for 

 supplying the skin and muscles of the anterior extremity, and resemble most the 

 median, spiral, and circumflex. The median descends and divides into large branches, 

 which pass into the substance of the hand, and give branches to the tendinous and 

 muscular parts, and send others towards the skin in the form of digital nerves. The 

 spiral gives some muscular branches in its course, and passes round to the outer side 

 of the arm-bone, and divides and sends a branch through the outer condyle to join 

 another, which is the principal continuation of the nerve, to terminate on the skin at 

 the outer margin and back of the hand. The circumflex passes upwards, beneath the 

 muscle resembling the broadest of the back, and gives a branch to the larger teres 

 muscle, and is then directed downwards, to terminate on the skin at the back of the 

 arm. Most of the nerves of the dorsal region enter principally into the structure of 

 the great shell ; the rest of the dorsal and sacral and caudal supply the posterior 

 extremity, the tail, and the reproductive organs externally. From the ninth dorsal 



