380 APPENDIX III 



SCROTUM (L. scrotum, pouch), the pouch in which the mammahan testes 

 he; the scrotum is homologous with the labia majora of the female. 



SEDIMENTARY (L. sedimentum, settling), in geology, referring to the rocks 

 which have been deposited in water or land depressions. The original 

 materials may be carbonates, mud, sand, or gravel which are 

 cemented or pressed into rock formations. They are the fossil bearing 

 rocks. 



Selachii (G. selachos, a shark), a group of elasmobranch fish, including 

 the sharks. 



SELLA (L. a seat or saddle), sella turcica, the depression of the skull in 

 which the pituitary rests. 



SEMI (L. half), combining form; semilunar, semipermeable, semispinahs. 



SEMILUNAR (L. semi, plus luna, moon), half moon-shaped ; specifically the 

 valves guarding the orifices of the arteries leaving the heart. 



SEMINAL (L. semen, seed), pertaining to the fluid medium of spermatozoa, 

 secreted by the testicular tubules and the glands associated with the 

 ducts; semen is the fluid. 



SEPTUM (L. sepes, a fence), a dividing partition; the septum between 

 the auricles; myosepta. 



Silurian (from Silures, a tribe in England), a geological period of the 

 Paleozoic, above the Ordovician, and below the Devonian. 



Sinanthropus (G. Sinai, Chinese, plus anthropos, man), a genus of ex- 

 tinct men, a skull of which was discovered near Peiping. 



SINUS (L, a bend or curve), in anatomy, a cavity in a bone or an en- 

 largement of a blood vessel; the sinuses of the head and face are 

 cavities in the bones, as the frontal or maxillary sinuses; also, 

 lymphatic sinuses; sinus venosus. 



Sirenia (G. seiren, a mermaid), an order of herbivorous aquatic mammals, 

 including the dugong and manatee. 



SOMA (G. body), a combining form; somatic, somatopleure. 



soMATOPLEURE (G. soma, plus plewa, side), the laj^er of the hypomere 

 lying next the ectoderm; it gives rise to the somatic peritoneum and 

 a part of the mesenteries. 



SOMITE (G. soma, body), a body segment; a metamere. 



Sphenodon (G. sphen, a wedge, plus odoiis, tooth), a genus and only 

 living representative of the order Rhynchocephalia, the most primitive 

 recent reptile. 



SPHENOID (G. sphen, a wedge, plus eidos, form), a wedge-shaped bone or 

 process; specifically, the sphenoid bones of the skull, developing from 

 the chondrocranium. 



SPIRACLE (L. spiraculum, an air hole), the modified first gill slit of the 

 sharks; the structure was carried over to the Crossopterj'gii, and to 

 the tetrapods as the middle ear and Eustachian tube. 



SPLANCH (G. splanchnon, viscera), a combining form; splanchnic, splan- 

 chnopleure. 



SPLANCH NOPLEURE (G. splancknon, plus pleura, side), the layer of the hypo- 

 mere in contact with the endoderm; it encloses the archenteron and 

 gives rise to the smooth muscle, mesentery, and visceral peritoneum. 

 The anterior part develops the heart and branchial (visceral) muscle. 

 Squalus (L. fish), a genus of small sharks; Squalus acanthias is the spiny 

 dogfish. 



