304 MICROSCOPIC A \AT()MY <>!' TllK <ili(,'A.\\ 



fibres of the first order, while the sympathetic axones ;ire 

 motor fibres of the second order. 



It must be noted that in the sympathetic ganglia of am- 

 phibians there are unipolar cells without dendrites. The one 

 process is to be regarded as an axone. It is surrounded by a 

 spiral fibre which brancht > and forms an end plexus around 

 the ganglion cells. These spiral fibres are derived from cells 

 lying at a distance, and represent motor fibres of the first order. 

 Among sympathetic ganglia are to be considered, the ganglion 

 ciliare, splenopalatinum, oticurn, and submaxillare. 



C. Nerve-endings. 



The nerve-endings are the final terminations of individual 

 neurones. By means of these the nervous system is put into 

 communication with other organs and tissues, and in the 

 nervous system itself individual neurones or segments are 

 joined together. It is through their agency that sensory im- 

 pulses are sent to the central nervous system, and motor im- 

 pulses transmitted from the nervous system to peripheral 

 organs. We distinguish free nerve-endings in which the much- 

 branched nerve filament receives or gives out impulses without 

 the intervention of other tissues ; and nerve-endings connected 

 with some specialized end apparatus. In the latter the nerve- 

 ending is combined with other tissues to form a special struct- 

 ure. We can classify nerve-endings according to the tissue 

 in which they have been formed. Thus we find nerve-endings 

 in: 1, epithelium; 2, connective tissue; 3, muscle; and 4, 

 nervous tissue. 



Finally, one may also consider nerve-endings from a physio- 

 logical standpoint ; but here unusual difficulties present them- 

 selves. A classification of nerve-endings according to their 

 functions is not practicable as long as we are ignorant of 

 the anatomical difference between centripetal and centrifugal 

 nerve fibres. For example, in glands we do not know which 

 endings are secretory and which are sensory. Also the division 

 of sensory endings according to their powers of transmitting 

 special sense impressions (temperature, pressure, pain, etc.) is 



