'12 DEVELOPMENT OF THE COMMON PHALANGER 



adult. No trace of the lachrymal grooves can be detected 

 externally, except, perhaps, the slight notching of the lip. 

 The eyelids give the eye an oval shape, and the slight pigmenta- 

 tion of the retina can be seen. The external ear is already well 

 developed, and a distinct little pointed pinna stands up from the 

 upper and posterior part of the meatus. The anterior limbs are 

 considerably further developed than in Embryo A, and the digits 

 almost meet in front of the chest. Distinct little claws can be 

 ■ detected on the digits. The hind limljs are much in advance of 

 those in Embrj'O A, and indications of the separate digits can be 

 distinctly made out. 



Embryo C (10 mm). Plate xxii., fig. 3. 



This embryo very closely resembles the preceding. The head 

 is here even more bent on the body. The mouth is almost 

 closed, and the tip of the tongue only but very slightly protruded. 

 The nose and eye are very similar to those in Embryo B, but the 

 ear is apparently a little better developed. The fore limbs are, 

 perhaps, very slightly better developed ; but in the hind limbs, 

 though the digits are all marked out, the first and second are less 

 clearly differentiated than in the preceding embryo. 



UpiJennis. — The epitrichial layer is moderately developed all 

 over the foetus. It is much less marked on the body proper than 

 on the head and fore limbs. It is especially thick ai'ound the 

 snout and anterior part of the lower jaw. The claws may now 

 be regarded as distinctly horny at the tips. The dental lamina is 

 -well marked in the fr'ont of the jaws. 



Skeleton. — The cartilaginous cranium is now fairly well 

 developed. The basi- and exoccipital regions are well chondrified, 

 as is also, to a considerable extent, the periotic capsules. From 

 the basisphenoidal region the trabecules can be traced forward to 

 the nasal septum with its related nasal cartilages, all of which are 

 already fairly developed. The alisphenoids are separately formed 

 as short rounded cartilaginous bars ; and the oi'bitosphenoids are 

 also already developed. The palate plates, though fairly well 

 formed, are widely apart, and the tongue is found between them, 



