GLOSSARY 683 



pedicle. The bony connexion between the lamina and centrum of a vertebra. 



peduncle. A fiber tract which connects the cerebellum with the brain stem. 



Peking man. A fossil species of man intermediate between the Java man and the 



Neanderthal. 

 pelvis. The basin-shaped ring of bone which connects back and leg bones. 

 penis. The male intromittent organ. 

 pepsinogen. A zymogen which when combined with hydrochloric acid forms 



pepsin. 

 peptone. A soluble derived protein formed by the hydrolysis of protein, 

 perennibranch. With persistent gills. 



pericardium. The membranous sac which encloses the heart. 

 perichondrium. The connective tissue membrane which surrounds cartilage, 

 periderm. The transient external layer of the mammalian embryonic epidermis, 

 perilymph. The liquid in the space between the membranous and the skeletal labyrinth 



of the internal ear. 

 perimysium. The delicate connective tissue membrane which surrounds a bundle of 



muscle fibers. 

 perineum. The floor of the pelvic outlet. 

 perineurium. The connective tissue covering a nerve cord, 

 periosteum. The connective tissue membrane which surrounds a bone, 

 peristalsis. The wave of contraction which passes along the intestine, 

 peritoneum. The serous membrane which lines the body cavity and covers the viscera, 

 petrosal. The petrous portion of the temporal bone. 

 Pfiueger's egg tubes. Cords of peritoneal cells which are said to grow into the stroma 



of the ovary. 

 phagocyte. A cell which ingests bacteria, 

 phalanx. One of the finger or toe bones, 

 phallus. The penis. 



pharynx. That part of the alimentary canal which connects mouth and esophagus, 

 photophore. A luminous organ, 

 photoreceptor. A sensory cell sensitive to light. 



phylogenesis. Racial history. The evolution of higher from lower animals. 

 pia mater. The innermost and most vascular of the three coverings of the central 



nervous system. 

 pilaster cells. Columnar supporting cells peculiar to fish gills. 

 pillar cells. Special columnar cells of Corti's organ located between the inner and 



outer rows of hair cells. 

 pineal body. The posterior epiphysis of the diencephalon. 

 pinna. The projecting portion of the external ear. 



pisiform. A pea-shaped proximal carpal bone on the ulnar side of the wrist. 

 pit organs. A pair of sensory pits anterior to the eyes of vipers. 

 pituitary gland. An endocrine organ attached to the infundibulum. 

 pituitrin. Extract of posterior lobe of pituitary gland, used to stimulate contraction of 



smooth muscle (uterus, etc.). 

 placenta. The mammalian organ of attachment and nutrition of the embryo, 

 placode. A local disc-like thickening formed as an anlage of an organ, 

 placoid scale. The typical elasmobranch scale with enamel and dentine layers. 

 plankton. Floating organisms which may be collected with a tow-net. 

 plantigrade. Flat-footed. 



plasma. The liquid portion of the blood, the serum and fibrinogen. 

 plasmodesm. A fine protoplasmic thread which connects two cells. 

 plastron. The ventral bony shield of the turtle. 



