THE INTEGUMENT 



665 



to obtain nourishment. The dermal scutes of ganoids, and the dermal 

 bones of higher forms arise entirely within the corium. Teeth are com- 

 posite structures composed of dentine, a hard sort of bone, from the 

 corium, overlaid with enamel from the epidermis. 



It is important that one does not confuse the term integument with 

 mere portions of the integument ; for example, the epidermis is merely 

 an outer histologic layer. The ectoderm is merely one of the germ 

 layers from which both integument and the nervous system arise. The 

 skin alone on such animals as have feathers, scales or fur, likewise 

 would not be the integument, but both skin and its immediate outer 

 covering would constitute such protective substance. The following 

 schematic arrangement is that commonly used in medicine: 



INTEGUMENT. 



Epidermis. 



1. Stratum corneum. 



2. Stratum lucidum. 



3. Stratum granulosum. 



4. Stratum mucosum. 



5. Stratum germinativum (Malpi- 



ghian layer). 



Secondary Epidermal Structures. 



Exoskeleton. H 



Hair. 



Nails, claws, hoofs, beaks. 



Feathers. 



Epidermal scales. 



Sensory nerve-endings 



Dermis. 

 (Commonly 

 called Corium) 



1. Papillary layer, made up of 



dense connective tissue. 



2. Reticular layer, made up of 



looser connective tissue. 



Secondary Dermal Structures. 

 Glands. 

 Pigment. 

 Blood vessels. 

 Lymph spaces. 

 Nerves. 

 Dermal scales. 



Note: The exoskeleton of vertebrates consists of bone, horn and 

 enamel. 



Bone originates in the corium (mesodermal). 



Horn and Enamel originate in the epidermis (ectodermal). 



In comparative anatomy the epidermis in turn is divided into two 



