376 



I'EXTBOOK OF ZOOLOGY 



coat and internal to this is the membranous peritoneum. In all 

 vertebrates, except mammals, the coelom consists of only two parts: 

 the pericardial cavity and the general abdominal cavity. In mam- 

 mals it is further divided into pericardial, thoracic, and aldominal 



cor 



Fig. 217. — Diagrammatic section of the human skin. Cor, stratum corneum ; 

 D, dermis ; gs, sebaceous gland ; M, Malpighian layer ; niu, muscle ; n, non- 

 meduUated nerve ; nm', nm", nm'", nina, and nmb, myelinated nerve fibers ; P, 

 papilla of hair ; Sc, hair shaft, u, fat tissue ; v and w, external and internal sheaths 

 of hair root; x and y, endings of nonmyelinated nerve fibers. (From Maximow and 

 Bloom, Histology, published by W. B. Saunders Co.) 



cavities. The first contains the heart, the second the lungs, and the 

 third the organs of the excretory, reproductive, and digestive systems. 



