148 



CELLS OF THE VERTEBRATE BODY 



intervals as to give a distinct cross-striped appearance to the cyto- 

 plasm. The cells are cylindrical, sometimes very long, and each 

 contains many nuclei. Fibrous connective tissue serves to bind 

 together striated muscle cells, and forms sheaths that enclose great 

 numbers of cells and so produce the visible muscles, such as the 

 gastrocnemius or the biceps (Fig. 81 C). These connective tissue 

 sheaths are continuous with the tendons by which muscles are 

 attached to bones. 



Nervous Tissue. — Nervous tissue is specialized in the direc- 

 tion of irritability. Its cells are differentiated for the purpose of 



Fig. 82. — Nervous tissues. A. Typical bipolar neurone from olfactory epi- 

 thelium. B. Showing transformation of bipolar neurone into type found in 

 dorsal root ganglia of spinal nerves. C. Multipolar neurone. D. Bundle of 

 medullated nerve fibers surrounded by fibrous connective tissue as in spinal 

 and cranial nerves. E. Portion of single medullated nerve fiber. The 

 sheath of myelin is interrupted at the nodes of Ranvier. The neurilemma 

 is continuous. F. Portion of non-medullated nerve fiber characteristic of 



autonomic nerves. 



o, axon; cb, cell body; d, dendrite; /c, fibrous connective tissue; 7ns, medullary sheath 

 of myeHn; n, neurilemma or nerve sheath; >if, nerve fiber; 7in, nucleus of neurilemma; 

 Rn, node of Ranvier. 



receiving stimuli, or changes in the environment; for transmitting 

 nervous impulses from one part of the body to another; and for 

 discharging these impulses to other kinds of cells in nerve-con- 

 trolled organs. The general functions can, therefore, be stated 

 as reception, transmission, and discharge. The result of these 

 activities of nervous tissue is the coordination of the organism as a 

 whole. A nerve cell, or neurone, is composed of a nucleus sur- 



