BY R. BROOM. 715 



stage of development being described from the sections of 

 Embryo E. 



Externnl characters. — Though the head is flexed on the chest, 

 the neck takes less part in the flexion than in the eai'lier stages. 

 The cheeks and upper lips are more compressed, and the whole 

 muzzle is more rounded than in Embryos B and C. The lips are 

 fused to a considerable extent, so that the cleft of the mouth 

 instead of being beneath the eye, as in Embryos B and C, is now 

 found beneath a point half-way between the nostril and the eye. 

 The eye is encroached on to a considerable extent by the epitri- 

 chial layer, and, though still oval in shape, appears appreciably 

 smaller. The ear resembles the earlier condition, but, like the 

 eye, is becoming encroached upon so that, though the pinna is still 

 quite distinct, the hollow of the external auditory meatus is largely 

 filled by the thickening epithelium. In the figure the fore limb 

 appears almost shorter than in Embryo C, but this appearance is 

 partly due to the skeletal elements meeting in front, and partly 

 to the increased epithelial growth, as the digits could now quite 

 easily interlock. The claws are well marked. The hind limbs 

 are not yet much more advanced than in Embryo C, but the 

 digits are rather more distinctly mapped out. 



Epidermis. — B(isides the increase of the epitrichial layer, the 

 xnost noteworthy additional feature met with in this stage is the 

 presence of well marked hair anlagen on the sides of the snout. 

 These are present as proliferations and dippings down of the 

 cells of the Malpighian layer, with condensations of the subjacent 

 mesoblastic cells. The dental lamina extends round a consider- 

 a,ble distance on both jaws, and the dental germs of the first upper 

 incisors are well differentiated. 



Skeleton. — Except in the more complete chondriti cation of the 

 various elements the skeleton diifers but little from that of 

 Embryo C. The coracoid is now chondrified to its inner end. 

 In the lower extremity the femur and pelvic elements, though not 

 yet cartilaginous, can be distinctly traced. Ossification is just 

 commencing in the maxillary bone. 



