68 F. W. THYNG 



SENSE ORGANS 



Eye 



The eye-ball is distinctly outlined, and the anlagen of the 

 eyelids form two prominent arches. The optic vesicle {Ves.op.), 

 its stalk (Op.s.), and the lens (L.) of the right eye are shown in 

 plate 3; the same structures on the left in plate 5. 



The optic stalk is slender and the lens is now devoid of a cavity. 

 Into the loose mesenchyma, occupying the vitreous chamber 

 extend the hyaloid artery and its branches. Other blood vessels 

 reach this chamber through the circular fissure at the margin of 

 the lens. 



Ear 



The fossa conchae (text fig. 1) is a depression rather broad 

 and shallow dorsally, but narrow and deep ventrally. The man- 

 dibular border of the fossa is formed by a fold especially promi- 

 nent in its ventral part where it presents a conspicuous projection. 

 This, the tuberculum tragicum, extends laterally and somewhat 

 toward the fossa. The ridge at the hyoid border of the fossa is 

 more prominent than that on the mandibular border and is 

 bounded caudally by the retroauricular groove. At the ventral 

 end of the ridge is a well marked protuberance which overhangs the 

 fossa directly opposite the tuberculum tragicum. It represents 

 the tuberculum antitragicum. The portion of the ridge dorsal 

 to this tubercle is the developing helix. In the central part of 

 the floor of the fossa is the low elevation which represents the 

 tuberculum membrane tympani of Hammar ('02). 



The lateral aspect of the right otic vesicle is represented in 

 plate 3 and the medial in plate 4. The stumps of the nerves 

 which innervate it are seen in plate 2. The utricular (Ut.), 

 saccular (Sac), and cochlear divisions (D.c), are not sharply 

 differentiated from one another, and the coalesced lamellae of the 

 lateral canal have not been absorbed as yet. The ductus endo- 

 lymphaticus widens into the saccus, and extends for a consider- 

 able distance dorsally. A peculiar anomaly occurs in this oto- 

 cyst; a short hollow diverticulum projecting from the utricle 



