BY R. BROOM. 709 



External anatomy. — As figured the foetus measures 8-2 mm., so 

 that allowing for a slight crushing of the back of the head, the 

 uninjured foetus probably measured 8'5 mm. The most striking 

 characteristic of the external appearance is the great proportional 

 development of the fore-quarters ; while the hind limbs are little 

 more that buds, without any indication of digits ; the fore limbs 

 are well developed, and have digits distinctly divided from each' 

 other, though not completel3^ Each digit is somewhat pointed, 

 and on section there are found to be distinct indications of the 

 developing claws. The antei'ior limbs are short and stout, and, 

 as seen from the front, are pretty widely apart, which is owing to 

 the skeletal elements of the two sides not having yet met in front 

 of the heart The tail is moderately stout, and towards the tip 

 the spinal cord is distinctl}' seen through the thin epidermis 



Epidermis. — The epidermis, though thin, is not uniformly so. 

 On the foi'e-limbs and back there is a very distinct epibrichial 

 layer, but towards the lower part of the body and in front it is 

 much less marked, and in some parts not very distinct. Claw 

 rudiments are well marked at the tips of the anterior digits. 



Skeleton. — The injured condition of the head makes it impossible 

 to say much more than that the parachordal cartilages are well 

 formed, and that there is as yet no chondrification of the auditor^' 

 capsule. Sufficient of Meckel's cartilage is preserved to show that 

 it is distinctly chondrified, although in the hyoid arch the process 

 is just commencing. In the cervical region the vertebral centra 

 and arches are already cartilaginous, and cartilage can be recog- 

 nised in the vertebral centra down to the upper lumbar region. 

 The upper ribs are fairly well chondrified, although no distinct 

 .sternum is as yet present. The scapula is well developed, as are 

 also the elements of the fore limbs, but the coracoid is only 

 distinctly formed at its outer part. In the clavicle ossification is 

 just commencing. The skeletal elements of the pelvis and hind 

 limbs are not yet distinctly differentiated. 



Kervous system. — The central canal of the spinal cord is 

 narrow in its anterior half, but its posterior half is on section 

 oval or pear-shaped. The cellular elements are much more 



