SYSTEM AND SUPRAllENAL BODIES IN THE SPARftOW. 757 



marked a-a and b-b in texfc-fig. 9 G call for some remark. Text- 

 tig. 12 shows the primary and secondary sympathetic chains 

 apparently quite disconnected. The primary has its usual posi- 

 tion at the dorso-lateral angle of the aorta, the secondary is 

 situated close against the spinal nerve, and lateral to the noto- 

 chord. Text-fig. 11, however, shows a section through the con- 

 nective between primary and secondary chains. The connective 

 at this stage is composed chiefly of nerve fibres, but along them 

 there are scattered cells, which are probably destined to forn\ 

 sheath cells. The two primary ganglia in this section will be 

 seen to have completely fused. 



F. Rami Communicantes. 

 The foregoing description of the development of the sympa- 

 thetic nervous system will explain how there has arisen a con- 

 siderable amoimt of confusion as to the rami communicantes in 

 birds, for it will be seen that in this group there are no less than 

 three distinct sets of connections associated Avith the central 

 nervous system and the outlying sympathetic. These are : — 



1. The strands of nerve cells which give rise to the primary 

 sympathetic cords. 



2. The constrictions of the dorso-lateral processes by which 

 the primary cords are attached to the secondaiy ganglia. 



3. The definite connections by which the secondary ganglia 

 become attached to the spinal nerves. 



Strictly speaking the term ramus communicans should be 

 restricted to the last of these three groups, but previous papers 

 and illustrations show that all these three forms have been thus 

 designated. Ganfini (5) goes so far as to use the terms primary, 

 secondary, and tertiary 7'ami communicantes for the three classes 

 of connections, but in view of their significance in neurology it 

 would seem preferable to apply the name only to those fibres 

 by which the definitive sympathetic is linked up with the mixed 

 spinal nerve. As the definitive ramies does not arise till about 

 the stage corresponding to that of a seven-day chick, it is evident 

 that any connection between the sympathetic and the central 

 nervous system, existing in earlier stages, must be looked upon 

 as an example of either the first, or the second, of the types of 

 connections above mentioned. As the history of their develop- 

 ment shows, the connections of groups 1 and 2 have only a 

 transient existence, with the possible exception of the connec- 

 tions in certain plexuses. 



The three types of connections are characterized more or less 

 definitely by their morphology. Those of the first group are 

 formed of (liscontinuous cells, though silver preparations show 

 that scattered nerve fibres occur in them. Connections of the 

 second type, on the other hand, are formed by compact masses 

 of cells, especially at their first appearance. In the. course of 

 their development they become elongated and may be narrowed 



Proo. Zool. Soc— 1923, No. L. 50 



