588 PROF. G. B. HOWES ON THE coHAcoiD [June 20, 



II. As to the Mammalian Coracoid. 



A leading feature in Mr. Lydekker's paper is the presumed 

 demonstration that in Bradypus the " so-called epicoracoid enters 

 to a small extent into the formation of the glenoid cavity." He 

 urges this, in forcible opposition to an assertion of my own that 

 " the exclusion of this element from the glenoid facet is one of its 

 most characteristic features ;" and from the context of his paper the 

 reader would be prone to conclude that I had laid this down as a 

 condition characteristic of all Mammals. In my original paper, to 

 which the assertion he transcribes is but a casual allusion, I 

 expressly stated ' that in the higher Placentalia the so-called epi- 

 coracoid " comes to enter into the formation of the glenoid facet in 

 proportion as the coracoid bar is suppressed," adding that " the 

 latter structure retires from thescene as the 'coracoid epiphysis' 

 of human anatomists." 



Mr. Lydekker asserts that in both the Dicynodont and the 

 Bradypodine the " so-called epicoracoid enters to a small extent 

 into the formation of the glenoid cavity ; " but while his figure of 

 the former depicts it as coutributing an altogether insignificant 

 share in the cavity, that of the latter represents it as contri- 

 buting wellnigh one linear half of it. There is an incongruity 

 here ; and in proceeding to deal with it I incorporate some 

 observations upon the Mammalian coracoid which have accrued 

 since my former paper wac written. 



My friend Mr. Oldfield Thomas has generously allowed me to 

 examine the material which passed through Mr. Lydekker's hands. 

 The latter gentleman infers that the coracoid of 81oths consists of 

 but one element (his so-called coracoid, Co , see figs. 1 d, 1 g), therein 

 implying that that element which I have claimed as the homologue 

 of the Monotreme's coracoid (his metacoracoid) is in them absent. 



There is in our National Collection a blade-bone of Cholaepus 

 didactylus (fig. 1 e) in which both coracoidal elements are well 

 represented; and it will be noted that the epicoracoid {Co') is 

 completely excluded from any share in the glenoid facet, like that 

 of both the Monotreme and the Eabbit, on comparison of which I 

 originally sought to reduce the pectoral girdle of all Mammals to a 

 uniform plan of structure. I find the metacoracoid {Co"), which 

 effects this exclusion, represented in a A'^ery young Bradypus 

 cucidliger hy a. feebly constituted fragment of bone (CV, fig. 1 c?) 

 wedged in between the epicoracoid and scapula. The epicoracoid 

 in this specimen is remote from the actual glenoid border, there 

 being present at this period of growth a considerable tract of 

 cartilage (the dotted area of fig. 1 d), into which the epi- and meta- 

 coracoidal centres are alike free to extend. 



The condition of this specimen is very nearly that of the Eabbit 

 (fig. 1 a) when first the metacoracoid {Co") appears. The 

 period of independent duration of this bone is, in the Placentalia, 



' Jouni. Anal. & Pliys. vol. xxi. p. 193. 



