178 



COMPARATIVE ANATOMY 



Fig. 147. — Diagram illustrating the Origin, Course, axd Termination of 

 THE Motor and Sensory Fibres of the Spinal Nerves, as well as the 

 Relations op the Sensory Collaterai. Fibres to the Points of Origin 

 OF THE "Ventral Roots. (After M. V. Lenhoss^k. ) 



Th|& spinal cord is shown as if transparent. The fibres of the ventral roots 

 Warise from the cells of the motor ventral cornua of the gray matter (a) and 

 end in fine branches on the striated muscle fibres (c). The spinal ganglion 

 {d) is shown relatively much larger than in reality, and in it only a single 

 unipolar nerve-cell is represented : the centripetal fibre of the latter is seen 

 entering the dorsal root, and at e bifurcates in the spinal cord into an anterior 

 (/)and a posterior (</) branch, each of which ends freely in the gray substance, 

 first giving off numerous collateral fibres {h). The centrifugal fibre of the cell 

 in the spinal ganglion forms a peripheral sensory fibre extending to the skin, 

 where part of it is shown ending in fine branches in the epidermis {i), another 

 part forming a coil in connection with a tactile corpuscle (k). 



roots remained distinct, as, in fact, is still the case in Amphioxus 

 and Petromyzon. 



The common nerw-tnmh formed by the junction of the two 



