THE OCCIPITAL BONE 51 
extends forward from the ventral margin of the foramen magnum. It is wide and 
flattened behind, narrower and thicker in front. The ventral surface is rounded. 
The cranial surface is concave and smooth; its posterior part supports the medulla 
oblongata, and its anterior part has a shallow cavity on which the ponsrests. The 
lateral borders are thin and sharp, and form the medial margin of the foramen 
lacerum. The anterior end has, in the young subject, a semicircular, flat, pitted 
surface which is attached to the body of the sphenoid bone by a layer of cartilage; 
in the adult there is complete fusion. On the ventral aspect of the Junction are the 
basilar tubercles (Tubercula basilaria) for the attachment of the ventral straight 
muscles of the head. 
The squamous part (Squama occipitalis)! is the somewhat quadrilateral mass 
Fic. 29.—Occtrrrat Bone or Cott; Front View. 
1, Depression of squamous part for cerebellum; 2, foramen magnum; 3, paramastoid process; 4, condyloid fossa; 
a, squamous part; 4, lateral part; c, basilar part; d, junction with interparietal bone; e, junction with parietal bone; 
f, junction with petro-mastoid part of temporal bone. 
situated dorsal to the lateral parts, from which it remains distinct till the second 
year. The external surface is crossed by a very prominent ridge, the nuchal crest 
(Crista nuchalis); the middle part of this is thick, transverse in direction, and forms 
the highest point of the skull when the head is in the ordinary position; laterally it 
becomes thinner and runs downward and forward to join the temporal crest.2, The 
crest divides the surface into two very unequal parts; the small dorsal area (Planum 
parietale) presents a median ridge which is the posterior part of the external parietal 
crest (Crista sagittalis externa); the large area ventral to the crest (Planum nu- 
chale) has a central eminence, the external occipital protuberance, on which the funic- 
ular part of the ligamentum nuche is attached. The internal surface is concave 
1 Also known as the supraoccipital. 
* The nuchal crest of this description is equivalent to the external occipital protuberance 
and superior nuchal line of man; it has been commonly termed the occipital crest, but is not the 
equivalent of that feature of the human skull. A curved line a little lower down, which is con- 
tinued on the paramastoid process, represents the inferior nuchal line of man. 
