SACOTGL 873 
And now to proceed to a more detailed description of the various 
regions of the Skull. The Occripur proper is formed by the Basi- 
occipital, right and left lateral and supra-occipital, all of which 
enclose the foramen magnum, through which passes the medulla 
oblongata (p 51), and, as in Reptiles, the Skull articulates by a single 
globular or kidney-shaped knob with the Atlas (cf. SKELETON, 
p- 848), the condyle being formed almost wholly by the basi- 
occipital, the lateral occipitals taking but little share in it, and thus 
constituting a fundamental distinction between the Amphibians on 
the one hand and Mammals on the other, where the articulation of 
the head with the neck is effected wholly by the lateral occipitals. 
SKULL oF Common Fowl FROM THE SIDE. (After Parker.) 
Part of the membranaceous roof between the supra-occipital and 
parietal bones frequently remains unossified and in the macerated 
Skull presents the appearance of a pair of fontanelles, which are 
- common features in Limicole and Anseres, but of variable occurrence 
in closely-allied genera. In the majority of Pigeons and also in 
some Owls and Parrots, the supra-occipital contains a single small 
median foramen for the passage of a blood-vessel, Further forwards 
the occiput joins the Basisphenoid, Alisphenoid and Periotic bones, 
this portion of the Cranium being roofed-in by the Parietals and 
Squamosals, the latter as a rule forming the posterior outer margin 
of the Orbits, and frequently continued into two lateral downward 
processes enclosing the temporal fossa. Of these the anterior, 
known as proc. orbitalis posterior, frequently combines with a similar 
outgrowth of the Alisphenoid, and in Cockatoos and Tinamous is 
continued forwards so as to meet a process of the Lacrymal bone, 
and thus forms an infra-orbital bridge ; while the posterior, known 
