682 Glossary 



Submucosa — the layer of connective tissue under a mucosal layer. 



Suture — the line of junction of bones in an immovable articulation such as in 



the skull. 

 Symbiosis — an association between two organisms in a manner that is beneficial 



to both. 

 Symmetry — the arrangement of parts. 



Sympathetic — a physiological division of the autonomic nervous system. 

 Symphysis — a union of two bones by means of cartilage. 

 Synapse — the junction of two neurons where a nerve impulse passes from one 



neuron to another. 

 Synapsis — the union of pairs of homologous chromosomes during the first division 



of meiosis. 

 Synarthrosis — an immovable articulation of two bones. 

 Synergist — a muscle which acts in cooperation with another to produce a move- 



nient. 

 Syngamy — union of gametes. 



Syrinx — modification of the trachea in birds to produce the vocal organ. 

 Systematics — the study of classification. 

 Systole — contraction of the heart. 



Taxonomy — the study of classification. 



Tendon — a tough cord of connective tissue that connects a muscle to another part. 



Test — an external shell. 



Testis — the male gonad. 



Tetanus — state of a muscle in continued contraction. 



Tetrad — a grouping of four chromosomes found in the first meiotic division. 



Thalamus — a portion of the brain, being a subdivision of the diencephalon. 



Thermocline — the region of most rapid temperature change in a thermally 



stratified lake. 

 Thoracic cavity — the chest cavity. 



Thrombus — a blood clot floating in the blood stream. 

 Tissue — a group of similar cells performing a specialized function. 

 Trachea — the windpipe. 

 Transverse plane — a plane crossing the long axis of the body and at right angles 



to both the median and frontal plane. 

 Triploblastic — with three germ layers. 



Trochophore — larva of certain marine annelids and related forms. 

 Trophozoite — one of the growth stages of a sporozoan. 

 Tuberosity — a prominence. 

 Tunica — a layer of tissue. 



U 



Unguis — a claw, nail, or hoof. 



