ON TllK MOHPHOLOOICAL CONSTITUTION OF LIMBS. 100 



corresponding sclerous parts in the lower animals, should be 

 the result of teleological subdivision of a single " diverging 

 appendage " or " archetj'pal element." I'rofessor Owen 

 virtually admits that these " teleological " elements have a 

 morphological value when he institutes an inqiury 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 ab-eady provided with a hiemal arch 

 in the series of transitory and persistent sclerous elements 

 developed in the third ])air of visceral laminai ; secondly, be- 

 cause the scapular girdle is invarialjly found to be developed 

 at or in the immediate neighl)ourhood 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 lamina? of the primordial vertebral system are passing 

 down towards the hi^mal margin. At first they resemble 

 lappet-like projections of the inferior margins of these lamina- : 

 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 lamina? 

 extend do^^'nwards, the lappets retain a position more or less 

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



• It is soiiicwhat roinarkiibli' thai tin- only euiliryolo;;ical evidence whicli 

 Professor <Jwen adduces in sujifiort of that portion of liis Doctrine of Limbs, 

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

 is a reference to a pas.sage in Hathke's Enticickeluntj d^r Schildkr^trn, in which 

 the author adduces iXw fundamtntal position of the bones of the shoulder — viz. 

 the posterior region of tlie neck - as a circumstance tendinp to explain their 

 iiltiniatf passage into the thomcic cavity. 



