Chap. VIII.] THE SKELETON. 159 



anterior part of the ex-occipitals, and fused into the general 

 mass of the brain-case. (3) The nasal chamber, with the median 

 septum nasi carrying forward the mid-plate of the spheneth- 

 moid. The septum gives off above and below horizontal wings 

 of cartilage forming the roof and floor of the cartilaginous nasal 

 chamber. The roof gives off a pre-nasal (p. n. p.) and an ali- 

 nasal process (a. n. p.), the floor a slender rhinal process (r. p.). 

 Anteriorly the septum gives off on each side a flattened vertical 

 plate meeting the horizontal wings above and below, and form- 

 ing the front wall of the chamber. (4) A bow-shaped orbital 

 bar on each side, constituted anteriorly by an antorbital or pala- 

 tine bar with a forward projecting process (a. o. p.), and laterally 

 a pterygoid bar which bifurcates posteriorly, the dorsal limb 

 passing into 4 the ventral crus of the suspensorium, and the 

 ventral articulating with the periotic capsule, and forming the 

 pedicle of the suspensorium. The pterygoid cartilage (pt. c.) is 

 partly invaded by the pterygoid bone (p. b.). (5) The suspen- 

 sorium lying between the squamosal and pterygoid bones, and 

 dividing dorsally into two crura, of which the ventral crus is 

 continuous with the pterygoid cartilage, and the dorsal crus is 

 attached to the periotic capsule (p. c.). 



Development and Homologies of Parts. A generalised description 

 of the development of the skull must suffice. The main features 

 of development are the same in all craniata (vertebrates with 

 skulls), but the details differ considerably, and for them the 

 student is referred to larger treatises. 



The parts of the skull are first indicated in mesoblastic tissue, 

 then developed in cartilage, and finally invaded or overlaid by 

 bone. Some parts are developed in relation to the brain-case, 

 others in relation to the sense-capsules, and others in relation 

 to the visceral arches. 



The first indication of the skull is the formation of two 

 parachordal plates underlying the mid and hind brain on either 

 side of the notochord (Fig. 51, A., ch.\ with which they com- 

 bine to form a continuous basilar plate (b. p.). In front of this 

 plate two bars are carried forwards from the parachordals, with 

 which they are from the first continuous in the fowl but not in 



