1892.] the Posterior Roots of some Spinal Nerves. 335 



axis in a somewhat backward as well as lateral direction ; those for 

 the fore-limb conversely slope somewhat forward as well as outward. 

 The dorsal axial line in the hind-limb rnns from the mid-dorsum 

 over the sacrum, past the back of the hip-joint, and along the outer 

 face of the thigh nearly to the knee. Of the dorsal axial line of 

 the fore limb only the most proximal part is described by the pre- 

 sent experiments ; that part runs from the mid-dorsum outwards 

 and forwards over the infra-spinous fossa of the scapula. The ventral 

 axial line of the hind-limb runs from the front of the body of the 

 pubes to the inner border of the thigh, arid descends along the 

 junction of the extensor and adductor groups of muscles nearly 

 to the knee. The ventral axial line of the fore-limb is in the present 

 experiments only followed for its proximal part ; that part lies on 

 the chest close below the clavicle. 



The position of these secondary axes having once been found (by 

 methods described in the paper) in the limb, it is not difficult to 

 examine the degree of apparent dislocation of each segmental field 

 and the nature of its distortion. In the segmentally anterior aspect 

 of the limb each segmental field has been curved so as to present a 

 very convex posterior edge, and the after-lap of the field is very large. 

 In the segmentally posterior aspect of the limb each segmental field 

 has been curved so as to present a very convex anterior edge, and the 

 fore-lap of the field is very large. The dorsal and ventral borders of 

 the fields are, in the limb, not much increased in length. Owing to 

 their serial arrangement along the secondary mid-dorsum and mid- 

 venter of the limb there is a secondary cross-lap of the fields there of 

 such a kind that a segmental field may there cross-lap with a seg- 

 inental field far distant from it in the segmental series ; thus the 9th 

 post-thoracic field may cross-lap with the 4th post-thoracic field. 



This dislocation of some of the segmental fields in the limb from 

 the mid-dorsum and mid-venter is apparent rather than real, and is not 

 a fundamental character of the limb segmentation, for it does not 

 occur in primitive types, e.g., is absent from the pelvic limb of the 

 Frog. 



Using the cutaneous field as a guide to the morphological position 

 of various points in the body, it is seen that the edges of the foot and 

 hand are, in the segmental fields of the limb, about midway between 

 the mid-dorsal and mid-ventral lines, and therefore must correspond 

 about with the lateral line of the trunk. The digits are therefore 

 buds from the region of the lateral line. 



The vulva and the anus are not at the posterior pole of the body, 

 but, like the umbilicus, are placed in the mid- ventral line. 



From the motor roots it is not easy to get evidence thafc the 1st 

 digit of the foot or hand is segmentally anterior to the 5th digit ; the 

 root supply of the intrinsic musculature of each is so similar. But 



