100 



MANUAL OF HISTOLOGY. 



series of the most striking transformations takes place in an originally 



purely cellular tissue. 



62. 



Another series of metamorphoses which may be mentioned here leads, 



it is supposed by a process 

 of fusion, to the formation 

 of many of the final ramifi- 

 cations of nerve-fibres. 



But the mode of origin of 

 the unbranched nerve-fibres 

 situated in the middle of 

 nervous trunks (fig. 107, 1) 

 is still, it must be granted, 

 a most obscure point. 



Nerve-fibres are usually 

 observed to divide in binary 

 order when near their ter- 

 mination (fig. 108). At 

 such points (at least appar- 

 ently) are situated stellate 

 cells, with usually three 

 processes (fig. 107, 2 a 1 , 

 b l . tr), one of which is 



Fig. 105. Connective tissue from between the muscles of the .. , ' , / . .,, .-, 



leg of a frog, a-e, connective-tissue cells ;/, flbrille ; and United by lUSlOU Wltll the 

 <7, bundles of the same ; A, network of elastic fibres. upper unbranched portion of 



the fibre, thus preparing the way for ramification of the latter. 



The neurilemma, or primitive sheath, a structureless tube which 



envelopes the mature nerve- 

 fibre (fig. 108), is probably, as 

 in the case of the sarcolemma 

 of muscle elements, laid down 

 from adjoining structures. 



63. 



The physiological relations 

 of the remaining tissue ele- 

 ments originating in the meta- 

 morphosis of cells, dealt with 

 in the second division, are so 

 very various that they must, 

 for the most part, be reserved 

 for future consideration. In 

 muscle-fibres and nerve-tubes 

 we have tissues of the highest 

 physiological dignity, while 

 the great group of connective 

 substances takes but a low 

 rank as investing or support- 

 ing tissues for the system. 

 The capabilities of transmuta- 

 tion are very various in the different tissues derived from the cell; but 

 at present our knowledge of the details of this subject is very imperfect. 

 Muscles and nerves, we are aware, are remarkable for the energetic 



Fig. 106. Elastic fibres from the human body. or. simple 

 and of the finer kind; c, a thick one, branching; 6, 

 fibrous network. 



