300 PHYSIOLOGY CHAP. 



one side only can regulate the movements of both wings ; while 

 the legs which come into play alternately have each an independent 

 regulating mechanism. The compensatory phenomena observed 

 after operating on one leg are undoubtedly due to sensations 

 coming from the sound leg. If this also is operated on the power 

 of standing is permanently lost. The labyrinth takes an important 

 part in these phenomena of compensation : if it is destroyed on 

 both sides, compensation disappears and never fully returns. 

 The cerebrum, on the other hand, has no influence in compensating 

 these motor disturbances. 



Trendelenburg's results agree with those obtained by other 

 experimentors on other animals. His observations differ in one 

 important respect from those previously recorded, viz. while 

 bilateral section of the dorsal roots of the legs causes muscular 

 atony of those limbs, so that they hang flaccid, bilateral section of 

 the dorsal roots that innervate the wings does not induce loss of 

 their muscular tone, so that when at rest they keep approximately 

 the normal position of flexion folded and raised on to the back 

 and neither hang flaccid nor trail the feathers on the ground. 

 The tone of the muscles to which this posture of the wings is due- 

 does not disappear even if the anterior brain is removed, or the 

 labyrinth destroyed. Trendelenburg concluded that the tone of 

 the wings is not reflex in origin. In some control experiments 

 Baglioni (1907), however, noted that the insensitive wing does not 

 behave at all like the normal wing. Even if the apaesthetic wing 

 does not hang or trail on the ground when the pigeon stands erect 

 or walks, like the wing paralysed by section of all its motor and 

 sensory nerves, it certainly does not oppose the same degree of 

 resistance to passive movements as a normal wing, nor is it raised 

 and lowered immediately like the normal wing. The insensitive 

 wing is, therefore, deficient in muscular tone. In order to explain 

 why the apaesthetic wing does not betray its atonic condition in 

 the erect posture or in walking, Baglioni suggests that the sensa- 

 tions coming from the leg reflexly excite tonic contraction of the 

 wing muscles, so that these are raised on to the back and do not 

 trail along the ground. 



V. The mode in which the fibres of the spinal roots are dis- 

 tributed after passing through the nerve plexuses to the skin and 

 subcutaneous tissues, and particularly to the muscles, is of more 

 than merely anatomical interest. It is intimately associated with 

 the simplest reflex functions of which the individual segments of 

 the cord are capable ; it has further a practical interest, as from 

 our knowledge of it it is possible from motor and sensory functional 

 disturbances to deduce conclusions as to the localisation of circum- 

 scribed lesions of the cord or the spinal roots. 



Anatomy tells us little of the special peripheral relations of the 

 sensory and motor fibres that emerge from each pair of roots. In 



