160 Prof. H. G. Seeley. The Shoulder Girdle and [June 



be cartilaginous. The weight of this comparison consists first in t 

 direct resemblance of plan between the Anomodontia and Ichth 

 sauria in the clavicular arch and the shoulder girdle, where 

 difference is essentially that in the former the precoracoid is ossifi 

 while in the latter there is a vacuity in the position which the pre- 

 coracoid occupies in the former. And secondly, although the 

 resemblance in detail in this region between the Anomodontia and 

 the Nothosauria is less close, as shown in the construction of the 

 scapula, there is a closer organic affinity between these types, which 

 gives importance to the resemblances which have been stated. 



The anatomical comparisons which have been made amount, I 

 submit, to as close an approximation to proof that the precoracoid 

 was represented by cartilage in Ichthyosaurus as could be given of 

 a structure which is necessarily not preserved in the skeletons in 

 which it has been argued to have existed. They may be thought to 

 justify the suggestion of a cartilaginous precoracoid in Ichthyosaurus 

 which was advanced in my paper. 



The Sauropterygia. 



I have regarded the Sauropterygian shoulder girdle as comprising 

 the same bones as the shoulder girdle in Ichthyosauria and Notbo- 

 sauria, and urge that the difference between them is that there is no 

 trace of a precoracoid in Plesiosaurs, even the cartilage in the 

 shoulder girdle indicated in those orders having disappeared. The 

 clavicular arch in all three orders appears to me to be formed of the 

 same elements, which I regard as being typically an interclavicle and 

 two clavicles. These identifications are contested by Mr. Hulke. who 

 advances the hypothesis that the bone which I regard as a scapula is 

 a precoracoid in its inner portion and a scapula in its outer portion ; 

 and secondly, the hypothesis that the bones which I regard as a 

 clavicular arch are not homologous with clavicular bones, but are a 

 new kind of arch, formed from omosternal bones. Both of these 

 hypotheses seem to me untenable, for the reasons presently to be 

 stated. In the first place, attention may be directed to the pre- 

 coracoid. Mr. Hulke has not explained why it is morphologically 

 necessary to find a precoracoid in Sauropterygia when its existence is 

 not affirmed by him in Ichthyosauria. He would apparently admit 

 (fig. 4, loc. cit., p. 241) that in Lacertilia the precoracoid loses its 

 individuality by union with the coracoid, and, as I have stated, there 

 are many examples which probably show such a condition among 

 extinct animals. But heie is a suggestion to blend the precoracoid 

 with the scapula, to which no parallel can be found, as I believe, in 

 true Reptiles, recent or fossil. It is not suggested by Mr. Hulke th t 

 any specimen exists in which there is a trace of a division of tie 



