CLEAVIGIE CHAP. 
Ww 
oe) 
ently not due to real resemblance. What has happened in the 
Monotremata is, that the prescapular fossa is so enormously 
expanded that it occupies the whole of the inner side of the 
blade-bone, while the subscapular fossa which, so to speak, should 
occupy that situation, has been thus pushed round to the front, 
where it is divided from the postscapular fossa by a slight 
ridge only. 
The clavicle is a bone which varies much in mammals. — It is 
sometimes indeed, as in the Ungulata, entirely absent ; in other 
forms it shows varying degrees of retrocession in importance ; it 1s 
only in climbing, burrowing, digging, and flying mammals that 
it is really well developed. 
In the higher Mammalia the coracoid' is present, but does 
not reach the sternum as in the Monotremata. It is known to 
human anatomists as 
the coracoid process 
of the scapula. It 
has been found, how- 
ever, by Professor 
Howes” and others, 
that this process 
really consists of 
two separate centres 
of ossification, form- 
Fia. 29.—Shoulder girdle, with upper end of sternum (inner, 
surface) of Shrew (Sorex), after Parker. x 7. a, Acro. INg two _ separate 
mion; ¢, coracoid; c/, clavicle; ec, partially ossified xi ; j 
: BE : S 
“epicoracoid ” of Parker, or rudiment of the sternal bonelets, which in 
extremity of the coracoid ; ma, metacromial process ; the adult become 
Ae aes “ ann Pcaieyare Dea ayn a a 
a caraed ermeeenecrareent os cnet at aa ee 
sr first sternal rib; sr, second sternal rib. (From each other and _ to 
epee sO eereay:) the scapula. These 
two separate bones have been met with in the embryo of Lepus, 
Seiurus, and the young of various other mammals belonging to very 
diverse orders, such as Edentates and Primates. The separation even 
occasionally persists in the adult. The question is, What is the 
relation of these bonelets to the coracoid of the Monotremata and 
to the corresponding regions of reptiles ? Professor Howes terms the 
lower patch of bone the metacoracoid and the upper the epicoracoid : 
1 To this category are perhaps to be referred cartilaginous pieces occurring in 
the Rabbit, Mus and Sorex (see Fig. 29 above). 
2 “On the Coracoid of the Terrestrial Vertebrates,” P.Z.S. 1893, p. 585. 
