356 Transactions of the South African Philosophical Society. 



coracoid, and it is also remarkable for the entire absence of the 

 clavicle. Whether the anterior of the two ventral bones is a pre- 

 coracoid or merely a process of the scapula has been answered in 

 different ways by different authorities. Though many have regarded 

 it as a precoracoid we may be pretty sure from what we now know 

 of the morphology of the precoracoid in primitive reptiles that the 

 bone in the ostrich is an anterior process of the scapula and is in no 

 way homologous with the true precoracoid of early forms. A bony 

 or cartilaginous precoracoid probably existed in all Stegocephalians, 

 and it was inherited by the earliest reptiles. The Synapsidan group 

 retained it in a well-developed condition owing to their having limbs 

 for walking with the body well off the ground. Thus we find it in 

 the Pareiasaurians, the Dinocephalians, the Therocephalians, the 

 Anomodonts, and the Cynodonts. It is even handed on to the 

 mammals and is present in Omithorhynchus and Echidna. It is 

 very doubtful, however, if any trace of it occurs in higher mammals. 

 In the other group of reptiles, the Diapsidan, it was very early lost, 

 and is only known to occur in the Pelycosauria, Mesosauria, and 

 Procolophonia. In no other Diapsidan reptilian order does any 

 trace of the precoracoid remain. Whatever may have been the 

 ancestor of the bird, it is scarcely doubtful that it was a well- 

 advanced Diapsidan reptile, and if the ancestor had already lost the 

 precoracoid it is impossible for the descendant to have acquired it 

 anew. Against the anterior ventral bone of the ostrich being the 

 precoracoid there is also the pretty conclusive fact that it never has 

 a distinct centre of ossification. 



So far as I am aware the only work that has been published on 

 the early condition of the ostrich's shoulder girdle is that by Miss 

 Lindsay. She has dissected ostrich embryos said to be of 4, 7, 10, 

 15, 21, 25, and 27 days' hatching, and describes and figures a number 

 of stages of the shoulder girdle. Unfortunately there is reason to 

 believe that some serious mistake has been made in the age of the 

 embryos. The embryo she figures as of 4 days is larger and more 

 advanced than one in my possession of 8 days' incubation. It is 

 possibly an embryo of 9 or 10 days' incubation. The one figured as 

 of 7 days is distinctly larger and more advanced than one I have of 

 11 days. Probably it is an embryo of 12 days' incubation. Both 

 figures are on too small a scale to show details accurately. In both, 

 three toes are very distinctly shown on the hind foot, though in my 

 specimens there is little external evidence of the second digit. 



In the "4-day embryo" Miss Lindsay states that the "scapula 

 and coracoid are not united," and also that " the coracoid and pre- 

 coracoid are separate." A figure is given of this condition. 



