322 THE AMERICAN NATURALIST. [VOL XXXII. 
fusion with adjacent elements might, however, pass into a 
mammalian prototype. 
Some of the peculiar adaptive features of this type are the 
very elevated position of the squamosals (as in certain plesio- 
saurs); the paroccipitals or opisthotics exhibit large posterior 
vacuities, as in Dicynodon, and are united with exoccipitals; 
basioccipitals narrow; the epiotics are said to be separate (1895, 
5, p. 77); the alisphenoids and orbitosphenoids are defined; 
laterally we observe descending plates of the pterygoids or 
“ transversg-palatine ” bones. 
The angular region of the jaw of Cynognathus is unfortunately 
wanting, but it is improbable that the placental type of angle 
was present. Seeley points out (1895, 5, p. 90) that the rudi- 
mentary mammalian angle may consist of the posterior border 
of the dentary, and concurs with Osborn! ¢hat the angle arose 
anteriorly on the lower border of the jaw (as perhaps in Micro- 
conodon, Amphitherium, and Peramus) and was subsequently 
shifted backwards. 
Remains of the shoulder girdle show that a coracoid (meta- 
coracoid) and epicoracoid with foramen were present (as in 
Dicynodon), and more striking still as a point of resemblance 
to the monotremes is the spine and acromion of the scapula, 
consisting of “the anterior edge of the scapula developed 
upward : (1895, 5, p. 92). 
Of the vertebra preserved (1895, p. 97) there are six cervi- 
cals, eighteen dorsals, five lumbars; thé first of these has the 
spine and odontoid process characteristic of the mammalian axis, 
the atlas being probably lost. The formula is estimated as: 
C.-6, D.-18, L._5, S—4. The writer has estimated the dorso- 
lumbar formula of the primitive mammal at D.=15, L.= 5, 
or D.L.=20. Thecervicals exhibit large intercentra (structures 
seen in a vestigial form in embryonic Insectivora and other 
mammals), to which, as well as to the centra, the heads of ribs 
are partly attached, certainly in the case of two vertebrae 
(op. cit., p. 99), while the rib tubercles unite with the pleurapo- 
physes of the vertebra posterior in true mammalian fashion. In 
the dorsal region (op. cit., p. 104) no intercentra are described; 
1 See Mesozoic Mammalia, p. 223. 
