688 coMPARArrvE anatomy 



tetany. Painful muscular spasms associated with calcium deficiency. 



thalamus. Gray matter located in the lateral walls of the diencephalon. 



thecodont. That type of dentition in which the teeth are lodged in sockets. 



theelin. The female sex hormone. 



thoracic duct. The main lymph channel which conveys lymph from the lower half of 



the body to the left jugular vein. 

 thrombin (fibrinogen). A hj'pothetical enzyme in clotted blood which converts 



fibrinogen into fibrin. 

 thymus. A ductless gland, largest in infancy, which lies below the sternum in the 



mediastinum. 

 thyroglossal duct. A rudiment of the connexion of the thyroid gland with the pharynx, 

 thyroid gland. An endocrine organ located on the sides of the trachea. 

 thyroxine. The iodine-containing hormone secreted by the thyroid gland. 

 tibia. The shin bone which carries the weight of the body to the ankle. 

 tigroid substance. The deeply-staining granular substance which forms the Nissl 



bodies. 

 tonus. The normal condition of tension of a muscle. 

 Tomaria. The free-swimming larva of Balanoglossus (Hemichordate). 

 trabeculae. The embryonic prechordal cartilages which enter into the formation of 



the basicranium. 

 trachea. The cartilaginous tube which connects the larynx with bronchial tubes. 

 tragus. The cartilaginous projection before the opening of the auditory meatus. 

 transverse septum. The connective tissue partition which separates the pericardial 



cavit}' from the abdominal cavity. 

 triconodont. A primitive t>^e of dentition in which three cusps in line occur, 

 tricuspid valve. The right atrio-ventricular valve. 

 trigone. A triangular area as of the bladder. 

 trilobite. A fossil crustacean extinct since the Carboniferous, 

 triquetrmn. A proximal carpal bone between the lunate and the pisiform. 

 trochanter. One of the two processes below the head of the femur. 

 trochlea. A pulley-like structure. 



trochophore. The swimming larval stage of some annelids. 

 trophoblast. The ectodermal portion of the fetal villi of mammalian embryos. 

 tr5T)sin. The protein-splitting enzyme secreted by the pancreas. 

 tuber cinereiun. A conical process of the subthalamus between the mammillary bodies 



and the infundibulum. 

 tuberculum impar. The anlage of the apex of the tongue. 

 tuberosity. A tuber-like process of a bone, 

 tunica. A covering tissue or coat. 



ultimobranchial (postbranchial ) bodies. Glands of unknown function derived from 



the last pair of pharyngeal pouches. 

 vunbilicus. The scar which marks the abdominal connexion of the umbilical cord. 

 imcinate. Hooked. 



imcus. The backward-bent anterior portion of the hjppocampal gyrus, 

 ungulate. Hoofed. 

 urachus. The canal which leads to the allantois and which becomes the median 



umbilical ligament. 

 ureter. The duct which connects the metanephros (kidney) with the bladder, 

 urethra. The outlet of the bladder. In the male the urinogenital passage. 

 uterus. The "womb" in which the fetus develops. 

 utriculus. That part of the static organ with which the semicircular canals connect. 



