922 MU. A. FHASER ON THE DEVELOPMENT OP THE 
Figs. 17-19. Sections of Sheep embryoes X 25. 
Fig. 17. Transverse vertical section of embryo 1 centim. in length (a 
little oblique), showing canalis cochlearis, cochlear division of 
the ganglion acusticum, recessus vestibuli, superior and external 
semicircular canals, primitive jugular vein, facial nerve, sulcus 
tubo-tympanicus and arteria stapedialis. 
Fig. 18. Obliquely transverse vertical section of embryo 1*4 centim. in 
length, showing cochlear and vestibular divisions of ganglion 
acusticum, periotic capsule, primitive jugular vein, facial nerve, 
stapes, arteria stapedialis, long crus of incus, sulcus tubo-tym¬ 
panicus, neck of malleus, chorda tympani (mandibular branch 
of seventh) and hyoidean cartilage. 
PLATE 56. 
Fig. 19. Longitudinal vertical section of embryo 2 centims. in length, 
showing cartilages of mandibular and hyoidean arches. Periotic 
capsule and semicircular canals, facial nerve with its chorda 
tympani branch and meatus auditorius externus. 
Figs. 20-21. Sections of Dog embryoes X 25. 
Fig. 20. Obliquely transverse vertical section of embryo 1 ‘3 centim. in 
length, showing hind brain, canalis cochlearis, sacculus hemi- 
sphericus, recessus vestibuli, superior and external semicircular 
canals, primitive jugular vein, facial nerve, arteria stapedialis, 
and sulcus tubo-tympanicus. (The cartilage .is not represented 
in this section although it was present.) 
Fig. 21. Longitudinal vertical section of embryo 2*5 centims. in length, 
showing cartilages of mandibular and hyoidean arches, periotic 
capsule, periotic process, facial nerve with mandibular (chorda 
tympani) branch, and meatus auditorius externus. 
Figs. 22-38. Sections of Eat embryoes X 25. 
Figs. 22-24. Sections from embryoes about 9 millims. in length. 
Fig. 22. Longitudinal vertical section parallel to middle line of head, 
showing periotic capsule with semicircular canals, ganglion 
acusticum, primitive jugular vein, facial nerve with its gan¬ 
glion, mandibular and hyoidean cartilages, stapes, arteria 
stapedio-maxillaris, sulcus tympanicus, gasserian ganglion with 
its maxillary and mandibular branches, eye and olfactory pit. 
Fig. 23. Obliquely vertical section showing canalis cochlearis, cochlear 
and vestibular divisions of ganglion acusticum, recessus vesti¬ 
buli, superior and external semicircular canals, periotic capsule, 
