THE 
MONTHLY MICROSCOPICAL JOURNAL. 
DECEMBER 1, 1872. 
I . — Description of the Plates illustrating Mr. W. K. Parhers 
Paper on the Development of the Crows Shull. 
(Continued from page 226.) 
[N.B. — The description of the various stages of the Crow’s Skull, and the first 
three Plates, will he fouud in the November number of this Journal, pages 
217-226.1 
DESCRIPTION OF PLATES. 
Plate XXXVII. — Structure of the skull of the Nestling of the Carriou Crow 
( Corvus corone ), one week old. The figures are enlarged one-half. Fig. 1. Basal 
view of skull and face. Fig. 2. Side view of skull and face, including the 
mandible, showing its outer aspect. Fig. 3. Upper view of the skull, upper jaw, 
and nasal sacs. Fig. 4. A longitudinally vertical section of skull and face, 
showing the brain-cavity, auditory bones, septum nasi, and cranio-facial axis. 
Fig. 5. End view of skull and lower jaw. Fig. 6. Inner view of right mandible, 
or lower jaw. Fig. 7. “Os hyoides,” or distal part and base of 2nd post-oral 
arch, and the whole of the third, with its basal element. 
Plate XXXVIII. — Figures illustrating the skull of a Fledged Nestling of the 
Rook ( Corvus frugilegus), natural size. Fig. 1. Basal view of skull, face, and 
nasal capsules. Fig. 2. Side view of skull and face, including outer view of man- 
dible. Fig. 3. Upper view of skull and upper jaw. Fig. 4. A longitudinally 
vertical section of skull and nasal capsules, showing cranial cavity, auditory mass, 
septum nasi, cranio-facial axis, and inner view of mandible. 
Plate XXXIX. — Skull of Fledged Nestling of Rook— continued. Fig. 1. 
End view of skull of a scarcely fledged Nestling. Fig. 2. Ditto of an older Nest- 
ling. Fig. 3. Nasal labyrinth, dissected out and seen from above. Fig. 4. Trans- 
versely vertical section of nasal capsule in front of lateral ethmoids. Fig. 5. A 
similar section, seen behind the lateral ethmoids. Fig. 6. Inner view of nasal 
capsule, as seen in a longitudinally vertical section. Fig. 7. “ Os hyoides.” 
II . — Proposal for a Standard of Comparison of the Magnifying 
Powers of Compound Microscopes. By J. E. Ingpen, Esq. 
(Read before the Royal Microscopical Society, Nov. 6, 1872.) 
Every worker with a telescope finds the necessity of ascertaining 
with considerable accuracy the magnifying powers of his instrument 
with its various eye-pieces. This is done by measuring the dia- 
meter of the reduced image of the object-glass in the eye-piece, 
when the telescope is focussed for parallel rays. The aperture of 
the object-glass, divided by the diameter of its reduced image, 
gives the magnifying power. The advantage of this method is, as 
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