ON THE MOEPHOLOGICAL CONSTITUTION OF LIMBS. 199 



corresponding sclerous parts in the lower animals, should be 

 the result of teleological subdivision of a single " diverging 

 appendage " or " archetypal element." Professor Owen 

 virtually admits that these "teleological" elements have a 

 morphological value when he institutes an inquiry into their 

 " special " and " serial homologies." 



3. It appears to me that the scapular girdle cannot be the 

 haemal arch of the occipital segment of the head firstly, 

 because that segment is already provided with a haemal arch 

 in the series of transitory and persistent sclerous elements 

 developed in the third pair of visceral laminae ; secondly, be- 

 cause the scapular girdle is invariably found to be developed 

 at or in the immediate neighbourhood of that part of the 

 trunk of the animal where it is ultimately situated ; and, 

 thirdly, because it is improbable that the exceptions to a 

 general law should be more numerous than the instances in 

 which it is adhered to.* 



The germs of the limbs make their appearance when the 

 ventral laminae of the primordial vertebral system are passing 

 down towards the haemal margin. At first they resemble 

 lappet-like projections of the inferior margins of these laminae ; 

 they extend along at least four or five of their segments, and 

 are situated in those regions of the body to which the future 

 limb is attached viz. in the pelvic and posterior region of 

 the neck, except in the fish, in which the pectoral lappets are 

 situated close behind the head. As the ventral laminae 

 extend downwards, the lappets retain a position more or less 

 elevated on the side of the trunk. At this stage they also 



* It is somewhat remarkable that the only embryological evidence which 

 Professor Owen adduces in support of that portion of his Doctrine of Limbs, 

 in which the anterior limb is assumed to be developed at or close to the head, 

 is a reference to a passage in Rathke's Entwickelung der Schildkroten, in which 

 the author adduces the fundamental position of the bones of the shoulder viz. 

 the posterior region of the neck as a circumstance tending to explain their 

 ultimate passage into the thoracic cavity. 



