510

2

acordingly macerated for the extraction of the skeleton, and has yielded the skull,
bones of the trunk, scapular arch, and furculum, right humerus, right femur, tibia,
and fibula.

Learning that Mr. John Hancock, the accomplished and artistic taxidermist of
Newcastle-on-Tyne, has extracted the bones of the extremities from a rare skin of Alca
impennis, I wrote for the loan of those of the left side, and was favoured by a prompt
and kind acquiescence, the bones being stated to be from a mature female bird.

I have thus at command the materials for a description of the complete osteology of
this most rare and now generally regarded as extinct bird.

In my 'Descriptive Catalogue of the Osteological Series contained in the Museum of
the Royal College of Surgeons of England,' I have briefly noticed characteristics of the
cranium, dorsal vertebrae, scapula, coracoid, femur, and tibia of an Alca impennis which
the founder of the collection, John Hunter, had succeeded in procuring ; Mr. Blyth
had previously made known the fact that the humerus "possessed a very small internal
cavity, while the tibia was completely filled with marrow" 2 ; and these are the only
published notices of the osteology of the bird with which I am acquainted.

! 1. Vertebral column.

In the present specimen there are twenty-two moveable vertebrae between the skull
and sacrum, the last nine supporting moveable ribs, of which the first two pairs have
free extremities ; the succeeding pairs of free pleurapophyses articulate with haemapo-
physes, and these with the sternum.

The sacrum appears to include fourteen vertebrae, of which the first supports a tenth
moveable pair of ribs, the last of the ordinary thoracic costal series : its haemapophysis
does not reach the sternum.

The caudal vertebrae are fourteen in number, of which the last three are blended
together, and the first, by its pelvic relations, might claim to belong to the sacral
series.

The centrum of the atlas, anchylosed as an odontoid process to the axis vertebra,
presents a pair of small facets for articulation with the posterior basal angles of its
proper neurapophyses ; but these are mainly supported by the hypapophysis, simulating
the body of the atlas, and with which they are confluent. The back part of the hypa-
pophysis offers a flat surface to the centrum of the axis, beneath which it is slightly
produced at its lower part, being here wedged into the notch between the true bodies of
the axis and the atlas. The fore part of the hypapophysis combines with the neurapophyses
to form the cup for the condyle of the occiput ; the cup is emarginate above, and
traversed by the ligamentous continuation of the "odontoid" in its way to adhere to the
upper part of the occipital ball. The atlantal neurapophyses diverge as they rise, and
are joined together above by a broad plate slightly arching across from one to the other

1 4to, 1853, vol. i.p.221, preps.nos.1150-1160. 2 Proc. Zool. Soc. November 14, 1837,p. 122.