174 ox THE CORACOIDAL ELEMENT IN ADULT SLOTHS. [Feb. 14, 



marked c in both are homologous ; each articulating with the 

 lower border of the front of the scapula, from which they are 

 partially separated by a foramen (/), and each entering into the 

 formation of the glenoid cavity. Xow in the Dicynodont the bone 

 marked c has usually been identified with the precoracoid. Ac- 

 cording, however, to Professor Howes ' the latter term should be re- 

 stricted to a portion of the clavicular arch, and the name epicoracoid 

 applied to the element under consideration. This emendation, if 

 properly authenticated, I should of course have been willing to 

 accept, had it not been for another consideration. Apart from 

 that consideration, we must call the coracoidal element in the 

 shoulder-girdle of the Sloth the epicoracoid. This is in harmonv 

 with the conclusion of Professor Howes, who in the paper cited 

 (p. 404) observes that " the coracoid process of the Slarsupialia 

 and Placentalia is the homologue of the ]\Ionotreme"s epicoracoid." 

 When, however, he proceeds to add that tlie exclusion of this 

 epicoracoid from the glenoid cavity is one of its most charac- 

 teristic features, I must take leave to differ from him. It is true that 

 in the Mouotremes (as shown in fig. 3 of the drawing) the so-called 

 epicoracoid (c) — which all are agreed as representing the epicora- 

 coid of the Dicynodont — is excluded from the glenoid cavity ; 

 but this appears to me to be due to its having been pushed for- 

 wards and bent downwards into the ventral plane of the body. 

 Both the Dicynodont (in spite of what is urged br Professor 

 Howes) and the Bradypodiue so-called epicoracoid enter to a small 

 extent into the formation of the glenoid cavity '. 



We have it, then, that the human coracoid process is homolo- 

 gous with the so-called epicoracoid of Bmclypus, Dicifnodon, and 

 Echidna ; while the element termed coracoid in the two latter, as 

 articulating with the sternum, represents the element so named 

 in the Sauropsida. Here, however, as has been pointed out to me 

 by my friend Mr. Thomas, a new difficulty arises. The coracoid 

 element was first named from the coracoid process of man, and 

 therefore, undoubtedly, the bone which we have called epicoracoid 

 is the true coracoid ; while the element to which the latter term 

 is applied in the Monotremes and Sauropsida is properly a meta- 

 coracoid. In spite of the difficulty which Avill probably arise in 

 obtaining the adoption of the latter term for the posterior ventral 

 moiety of the Sauropsidan pectoral girdle, I therefore suggest 

 that we must for the future term that element the metacoracoid, 

 and restrict the term coracoid to the coracoid process of the higher 

 Mammals and the bone which has been termed epicoracoid in 

 Monotremes and Dicynodontsl 



1 Journ. Anat. Pbys. vol. xsvi. p. 403 (1S93). 



^ I may mention that I am indebted to Professor Howes for pointing out 

 that I have incorrectly identified the acromion in the scapula of Bicynodon, 

 the true acromion being the one lettered a in the accompanying figure. 



^ Professor Howes has been good enough to point out to me that Sabatier 

 has ideulified a rudiment of l.iie metacoracoid in the human scapula (see 

 Howes, op. vif. vol. xxi. p. 100). 



