146 



THE SKULL. 



[CHAP. 



intimately with the cranial walls. The basicranial plate 

 grows up as an arch over the occipital region of the skull, 

 and coalescing with the auditory capsules gives rise to the 

 primordial skeleton of the occipital, periotic, and basi- 

 sphenoidal regions of the skull : the parietal and frontal 

 regions being afterwards completed by ossification in mem- 

 brane surrounding the cranial cavity. 



FIG. 51. Elements of skull (seen from below) of an embryo Pig two-thirds of an 

 inch long, fa.ch parachordal cartilage ; nc notochord ; an auditory capsule ; py 

 pituitary body; tr trabeculse ; c.tr trabecular cornu ; pn prenasal cartilage; en 

 external nasal opening ; ol nasal capsule ; p.p palatopterygoid tract inclosed in 

 the maxillopalatine process; mn mandibular arch; hy hyoid arch; th.h first 

 branchial arch ; -ja facial nerve ; Ba glossopharyngeal; 8 vagus ; 9 hypoglossal. 



Besides the parts composing the cranium proper, the 

 Mammalian skull is completed by the labial cartilages, the 

 meaning of which is still very obscure, and a series of three 

 paired descending cartilaginous bars or arches, developed in 

 the visceral laminae, constituting the sides of the face and 

 neck. 



The first visceral (mandibular) arch divides itself into 

 a short proximal or dorsal, and a much longer distal or 

 ventral end (Meckel 's cartilage}. The first sends out 

 forwards towards the roof of the mouth-cavity, a process 



