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composed : this sheath is moulded to the shape of the osseous 
mandibles, being formed by a vascular substance covering these 
parts, and its margins are frequently provided with horny pro- 
cesses or laminae secreted by distinct pulps, analogous in this 
respect to the whalebone laminae of the whale.” To this is 
added the subjoined singularly apposite quotation from Greoffroy 
St. Hilaire, fit. 44 Systeme Dentaire des Mammiferes et des 
Oiseaux,” 8vo, 1824: — 
44 In a foetus of a parroquet, nearly ready for hatching, the 
margins of the bill are beset with while and round tubercles, 
arranged in a regular order, about seventeen in the upper jaw, 
the foremost on the mid- line. These tubercles are not indeed 
implanted in the alveolar border, but form part of the sheath 
of the bill. Under each tubercle, however, there is a gela- 
tinous pulp, like that of a tooth, but resting on the edge of the 
jawbones, and every pulp is supplied by vessels and nerves 
traversing a canal in the substance of the bone. These tuber- 
cles form the first margins of the mandibles, and their remains 
are indicated by canals in the horny sheath subsequently formed, 
which contain a softer material, and which commence from 
small foramina in the margin of the bone.” 
If, then, we accept Professor Owen’s interpretation as regards 
the embryonal character qf the long tail and the free digits of 
the wings in Archceopteryx that it is a true bird, but with 
44 a retention of a structure embryonal and transitory in the 
modern representatives of the class and a closer adhesion to 
the general vertebrate type,” then it is fair to assume that 
the presence of teeth in the mandible of such a bird is equally 
admissible both on the evidence furnished by the embryo of a 
living bird, the parroquet, and also on the grounds of a closer 
adhesion to the general vertebrate type. 
But, it may be urged, 44 your proposition that the Archceo- 
pteryx had teeth is a pure assumption. Show me some evidence 
of a fossil bird whose head and skeleton are in juxtaposition 
so as to leave no reasonable doubt of their unity.” Happily for 
our argument, this is exactly what Professor 0. C. Marsh has 
succeeded in doing in the case of two distinct bird-remains 
from the Cretaceous shale of Kansas.* 44 The type species of 
this group, Ichthyornis dispar (Marsh), had well-developed 
teeth in both jaws. These teeth were quite numerous, and im- 
planted in distinct sockets. They were small, compressed, and 
pointed, and all of those preserved are similar. Those in the 
lower jaws number about twenty in each ramus, and are all 
more or less inclined backward. The series extend over the 
* a On a New Sub-class of Fossil Birds” ( Odontornithes ). By Professor 
0. C. Marsh, Yale College, Ct., U.S.A. u Silliman’s Journal,” vol. iv. p. 
344, Oct. 1872, and vol. v. p. 74, Jan. 1873. 
