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68 ANATOMY.
tres of ossification. There is a natural division of these o.ssific points
into a posterior (postsphenoid) and an anterior (presphenoid) portion.
TJte Hc!/a Turcka and the great wings belong to the former of these
divisions, while that portion of the body in front of the olivary process
and the lesser wings belong to the latter. This division is found com-
plete and persistent throughout life in many of the lower animals. At
about the eighth week of embryonal life ossification commences in the
postsphenoid division. There is one nucleus for each great wing (ali-
sphenoid), including the external })terygoid plates. About the same
time two nuclei appear for the posterior part of the body of the bone
(basLsphenoid). These unite about the fourth month. After this union
Fig. 24.
a
A, the sphenoid bone of ii fu'tus, aged about three months, is seen from above. The great wings are
ossified ; the body has two round granules of bone beneath the sella turcica, and the rest of it is
cartilaginous. In the small wings, which are formed from a single centre, the ossification has
encircled the optic foramen, and a small suture is distinguishable at its posterior and inner side.
The internal pterygoid processes are still separate (C<) in the preparation from which the draw-
ing was made.— I-!. This figure is copied from Meckel (Arvhiv, lid.i. Taf. vi. F. 23). It is stated to
be from a fcutus at the middle of the sixth month. The two granules for the body are united, and
a trace of their union is observable in the notch in front. The lateral projections of the body ('')
aie separate pieces.— (' is a sketch of the back part of the preparation shown in A. The internal
pterygoid process, which was united only by cartilage to the rest of the bone, has been drawn
aside.— D. This figure represents the sphenoid at the usual period of birth. The great wings are
separate. The anterior sphenoid is joined to the body.
1. The great wings; 2. The small wings; 2*. x\dditional nuclei for the small wing; 3. The body : 4.
The internal pterygoid process; n. The lateral processes of the body.
two other centres appear, from whicii are formed the tongue of the bone
(basitemporal).
The Interudl Pfcri/f/olfl Plate arises from two separate points of
ossification, which a])pear about the fourth month. The internal plates
unite with the external pterygoid plates about the fifth or sixth month,
and are analogous to the ])tervgoid bones of some animals, in which
thev remain .separate throughout life. In the anterior (presphenoid)
division ossification commences about the eighth or ninth week by two
luiclei, which are
inside of the optic fiu'amina, and form the ])resphenoidal portion of
the body of the bone. Some authors describe this portion of the bone
as developed from one centre of ossification, while others say that it is
formed from the same centres of
generally after birth.
