SKULL 



875 



And now to proceed to a more detailed description of the various 

 regions of the Skull. The Occiput proper is formed by the Basi- 

 occipital, right and left lateral and supra-occipital, all of Avhich 

 enclose the foramen magnuni, through which passes the meckdla 

 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 betAveen the Amphibians on 

 the one hand and Mammals on the other, Avhere the articulation of 

 the head with the neck is effected wholly by the lateral occipitals. 



s.o. 



qj. I lap. 



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 aj^pearance of a pair of fontanelles, which are 

 common features in Limicolai and Anseres, but of variable occiu-rence 

 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 jjassage of a blood-vessel. Further forwards 

 the occi2)ut 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 tAvo lateral downward 

 processes enclosing the temporal fossa. Of these the anterior, 

 known as proc. orbitalis j^osterior, frequently combines with a similar 

 outgrowth of the Alisphenoid, and in Cockatoos and Tinamous is 

 continued forwai"ds so as to meet a process of the Lacrymal bone, 

 and thus forms an infra-orbital bridge ; while the posterior, known 



