secreted layer 



serose gland ce 



Sharpey's fibers 



epidermis 

 ^stratum loxum 



horizontal and 

 vertical fibers of T 

 stratum compactum 



nerve of sensory organ 



fibrous dermis 



pigment cell 

 fibroblost or mesenchyme cell 



B 



Figure 8-19. The skin of eiasmobronchs. A, section of epidernnis of fhe ray, Raja punctata; 

 B, section of skin of Squo/us showing fibrous divisions of the dermis; C, sensory organ of epidermis 

 of Squo/us ocanthios. (After RabI, 1931) 



dermis 



intercellular matrix 



can be described. The denticle (Figure 8-22) consists of an 

 enamel cover over a dentine tubercle containing a pulp 

 cavity. This tubercle is attached to a dentine or bony basal 

 plate set in the dermis. The terms enamel, dentine, and 

 even bone refer to huinan materials; the first two to parts 

 of the tooth. 



granular cell 

 thread ce 



basement 

 membrane 



B 



cuticle 

 thread or club ce 



anchor strand of 



granular cell IQ 



germinal cell 



pycnotic nuclei of dead outer layer 



fibrous dermal layer 



Figure 8-20. Development of the skin of the lamprey. A, skin of 10- 

 mm larva; B, skin of 90-mm lamprey; C, epidermis and part of dermis 

 of adult. 



Enamel Enamel can be described in terms of its crystalline 

 structure and low organic content; it does not contain cell 

 spaces. It is also described in terms of its embryological ori- 

 gin, being a product of an ectodermal enamel organ. In dis- 

 cussing the scales of various fishes, there is considerable 

 doubt as to whether the smooth, glassy material on the outer 

 surface of the tubercles is enamel and the interior substance 

 dentine. These hard materials may be only analogous pro- 

 ducts to those of the human tooth. 



The question whether or not the selachians possess en- 

 amel has been much discussed with divergent conclusions. 

 The enamel-like materials of lower vertebrates agree with 

 dentine in terms of the orientation of their hydroxyapatite 

 crystals, but the birefringence of these materials is as a rule 



thread cell 



slime or mucous 



bladder cell 



^1 germinal epithelium 

 -^basement membrane 

 pigment cell 



Figure 8-21. Skin of Myxine (After Schreiner). 



SCALES • 227 



