306 GLOSSARY OF EMBRYOLOGICAL TERMS 



Transverse Neural Fold — continuation of lateral neural folds (ridge) of early 

 frog embryo around anterior neuropore. (Syn., transverse medullary 

 fold or ridge.) 



Trigeminal Ganglion — cranial (V) ganglia which consist of motor and 

 sensory portions and arise from segments of the most anterior crest 

 in conjunction with cells from inner (ganglionic) portion of corre- 

 sponding placode. Give rise to ophthalmic, mandibular, and maxillary 

 branches, associated with rhombencephalon at level of greatest width 

 of fourth ventricle. 



Trochlearis Nerves — cranial (IV) motor nerves which arise from dorsal sur- 

 face of brain near isthmus, coming from medullary neuroblasts and 

 innervating superior oblique muscles of eye. 



Truncus Arteriosus — anterior continuation of buibus arteriosus beneath 

 foregut, divided in antero-posterior direction by a septum which is 

 continuous through buibus to ventricle; gives off external carotids to 

 mandibular arches and second, third, and fourth aortic arches which 

 join dorsal aorta. (Syn., ventral aorta.) 



Tuberculum Posterius— a thickening in floor of brain at region of anterior 

 end of notochord, representing posterior margin of diencephalon. 



Tubo-tympanic Cavity — remnants of dorsal parts of first pair of visceral 

 (hyomandibular) pouches and lateral walls of pharynx, connecting 

 pharynx and middle ear, represented by Eustachian tube of adult bird 

 or mammal. 



Tubules — See under specific names such as Collecting, Mesonephric, Pro- 

 nephric. Seminiferous. 



Tunica Albuginea — See Albuginea of Testis. 



Tympanic Cavity — cavity of middle ear, a vestige of hyomandibular pouch. 

 (See Tubo-tympanic Cavity.) 



Tympanic Membrane — membrane made up of ectoderm, mesenchyme, and 

 endoderm which separates tympanic cavity from exterior. (Syn., ear 

 drum.) 



Urinary Bladder- — endodermally lined vesicle derived from hindgut, ho- 

 mologous to allantois of chick. Connected with mesonephric (excre- 

 tory) ducts of frog only through cloaca. 



Uriniferous Tubule — functional kidney tubule of mesonephros. 



Urodele — tailed amphibia (e.g., salamanders). (Syn., caudata.) 



